Fix bugs related to --posix shell option (re: 921bbcae, f45a0f16)

This fixes the following:
1. 'set --posix' now works as an equivalent of 'set -o posix'.
2. The posix option turns off braceexpand and turns on letoctal.
   Any attempt to override that in a single command such as 'set -o
   posix +o letoctal' was quietly ignored. This now works as long
   as the overriding option follows the posix option in the command.
3. The --default option to 'set' now stops the 'posix' option, if
   set or unset in the same 'set' command, from changing other
   options. This allows the command output by 'set +o' to correctly
   restore the current options.

src/cmd/ksh93/data/builtins.c:
- To make 'set --posix' work, we must explicitly list it in
  sh_set[] as a supported option so that AST optget(3) recognises
  it and won't override it with its own default --posix option,
  which converts the optget(3) string to at POSIX getopt(3) string.
    This means it will appear as a separate entry in --man output,
  whether we want it to or not. So we might as well use it as an
  example to document how --optionname == -o optionname, replacing
  the original documentation that was part of the '-o' description.

src/cmd/ksh93/sh/args.c: sh_argopts():
- Add handling for explitit --posix option in data/builtins.c.
- Move SH_POSIX syncing SH_BRACEEXPAND and SH_LETOCTAL from
  sh_applyopts() into the option parsing loop here. This fixes
  the bug that letoctal was ignored in 'set -o posix +o letoctal'.
- Remember if --default was used in a flag, and do not sync options
  with SH_POSIX if the flag is set. This makes 'set +o' work.

src/cmd/ksh93/include/argnod.h,
src/cmd/ksh93/data/msg.c,
src/cmd/ksh93/sh/args.c: sh_printopts():
- Do not potentially translate the 'on' and 'off' labels in 'set
  -o' output. No other shell does, and some scripts parse these.

src/cmd/ksh93/sh/init.c: sh_init():
- Turn on SH_LETOCTAL early along with SH_POSIX if the shell was
  invoked as sh; this makes 'sh -o' and 'sh +o' show expected
  options (not that anyone does this, but correctness is good).

src/cmd/ksh93/include/defs.h,
src/cmd/ksh93/include/shell.h:
- The state flags were in defs.h and most (but not all) of the
  shell options were in shell.h. Gather all the shell state and
  option flag definitions into one place in shell.h for clarity.
- Remove unused SH_NOPROFILE and SH_XARGS option flags.

src/cmd/ksh93/tests/options.sh:
- Add tests for these bugs.

src/lib/libast/misc/optget.c: styles[]:
- Edit default optget(3) option self-documentation for clarity.

Several changed files:
- Some SHOPT_PFSH fixes to avoid compiling dead code.

src/cmd/ksh93/include/shell.h

@@ -60,6 +60,33 @@ typedef void	(*Shinit_f)(Shell_t*, int);
 union Shnode_u;
 typedef union Shnode_u Shnode_t;
 
+/*
+ * Shell state flags. Used with sh_isstate(), sh_onstate(), sh_offstate().
+ * See also shell options below. States 0-5 are also used as shell options.
+ */
+#define SH_NOFORK	0	/* set when fork not necessary */
+#define	SH_FORKED	7	/* set when process has been forked */
+#define	SH_PROFILE	8	/* set when processing profiles */
+#define SH_NOALIAS	9	/* do not expand non-exported aliases */
+#define SH_NOTRACK	10	/* set to disable sftrack() function */
+#define SH_STOPOK	11	/* set for stopable builtins */
+#define SH_GRACE	12	/* set for timeout grace period */
+#define SH_TIMING	13	/* set while timing pipelines */
+#define SH_DEFPATH	14	/* set when using default path */
+#define SH_INIT		15	/* set when initializing the shell */
+#define SH_TTYWAIT	16	/* waiting for keyboard input */
+#define	SH_FCOMPLETE	17	/* set for filename completion */
+#define	SH_PREINIT	18	/* set with SH_INIT before parsing options */
+#define SH_COMPLETE	19	/* set for command completion */
+#define SH_INTESTCMD	20	/* set while test/[ command is being run */
+#define SH_XARG		21	/* set while in xarg (command -x) mode */
+
+/*
+ * Shell options (set -o). Used with sh_isoption(), sh_onoption(), sh_offoption().
+ * There can be a maximum of 256 (0..0xFF) shell options.
+ * The short option letters are defined in optksh[] and flagval[] in sh/args.c.
+ * The long option names are defined in shtab_options[] in data/options.c.
+ */
 #define SH_CFLAG	0
 #define SH_HISTORY	1	/* used also as a state */
 #define	SH_ERREXIT	2	/* used also as a state */
@@ -72,7 +99,9 @@ typedef union Shnode_u Shnode_t;
 #define SH_NOUNSET	9
 #define SH_NOGLOB	10
 #define SH_ALLEXPORT	11
+#if SHOPT_PFSH
 #define SH_PFSH		12
+#endif
 #define SH_IGNOREEOF	13
 #define SH_NOCLOBBER	14
 #define SH_MARKDIRS	15
@@ -95,10 +124,17 @@ typedef union Shnode_u Shnode_t;
 #define SH_DICTIONARY	30
 #define SH_PIPEFAIL	32
 #define SH_GLOBSTARS	33
-#define SH_XARGS	34
 #define SH_RC		35
 #define SH_SHOWME	36
 #define SH_LETOCTAL	37
+#if SHOPT_BRACEPAT
+#define SH_BRACEEXPAND	42
+#endif
+#define SH_POSIX	46
+#define SH_MULTILINE	47
+#define SH_LOGIN_SHELL	67
+#define SH_NOUSRPROFILE	79	/* internal use only */
+#define SH_COMMANDLINE	0x100	/* bit flag for invocation-only options ('set -o' cannot change them) */
 
 /*
  * passed as flags to builtins in Nambltin_t struct when BLT_OPTIM is on