Fix more compiler warnings, typos and other minor issues (#260)

Many of these changes are minor typo fixes. The other changes
(which are mostly compiler warning fixes) are:

NEWS:
- The --globcasedetect shell option works on older Linux kernels
  when used with FAT32/VFAT file systems, so remove the note about
  it only working with 5.2+ kernels.

src/cmd/ksh93/COMPATIBILITY:
- Update the documentation on function scoping with an addition
  from ksh93v- (this does apply to ksh93u+).

src/cmd/ksh93/edit/emacs.c:
- Check for '_AST_ksh_release', not 'AST_ksh_release'.

src/cmd/INIT/mamake.c,
src/cmd/INIT/ratz.c,
src/cmd/INIT/release.c,
src/cmd/builtin/pty.c:
- Add more uses of UNREACHABLE() and noreturn, this time for the
  build system and pty.

src/cmd/builtin/pty.c,
src/cmd/builtin/array.c,
src/cmd/ksh93/sh/name.c,
src/cmd/ksh93/sh/nvtype.c,
src/cmd/ksh93/sh/suid_exec.c:
- Fix six -Wunused-variable warnings (the name.c nv_arrayptr()
  fixes are also in ksh93v-).
- Remove the unused 'tableval' function to fix a -Wunused-function
  warning.

src/cmd/ksh93/sh/lex.c:
- Remove unused 'SHOPT_DOS' code, which isn't enabled anywhere.
  https://github.com/att/ast/issues/272#issuecomment-354363112

src/cmd/ksh93/bltins/misc.c,
src/cmd/ksh93/bltins/trap.c,
src/cmd/ksh93/bltins/typeset.c:
- Add dictionary generator function declarations for former
  aliases that are now builtins (re: 1fbbeaa1, ef1621c1, 3ba4900e).
- For consistency with the rest of the codebase, use '(void)'
  instead of '()' for print_cpu_times.

src/cmd/ksh93/sh/init.c,
src/lib/libast/path/pathshell.c:
- Move the otherwise unused EXE macro to pathshell() and only
  search for 'sh.exe' on Windows.

src/cmd/ksh93/sh/xec.c,
src/lib/libast/include/ast.h:
- Add an empty definition for inline when compiling with C89.
  This allows the timeval_to_double() function to be inlined.

src/cmd/ksh93/include/shlex.h:
- Remove the unused 'PIPESYM2' macro.

src/cmd/ksh93/tests/pty.sh:
- Add '# err_exit #' to count the regression test added in
  commit 113a9392.

src/lib/libast/disc/sfdcdio.c:
- Move diordwr, dioread, diowrite and dioexcept behind
  '#ifdef F_DIOINFO' to fix one -Wunused-variable warning and
  multiple -Wunused-function warnings (sfdcdio() only uses these
  functions when F_DIOINFO is defined).

src/lib/libast/string/fmtdev.c:
- Fix two -Wimplicit-function-declaration warnings on Linux by
  including sys/sysmacros.h in fmtdev().

src/lib/libcmd/cat.c

@@ -57,7 +57,7 @@ static const char usage[] =
     "converted back to the native encoding. Multibyte characters in the "
     "current locale are treated as printable characters.]"
 "[A:show-all?Equivalent to \b-vET\b.]"
-"[B:squeeze-blank?Multiple adjacent new-line characters are replace by one"
+"[B:squeeze-blank?Multiple adjacent new-line characters are replaced by one"
 "	new-line.]"
 "[D:dos-output?Output files are opened in \atext\amode which inserts carriage"
 "	returns in front of new-lines on some systems.]"

src/lib/libcmd/fold.c

@@ -43,7 +43,7 @@ static const char usage[] =
 		"to zero.  \bfold\b will not insert a newline immediately "
 		"before or after a carriage-return.]"
 	"[+backspace?If positive, the current count of line width will be "
-		"decremented by  one.  \bfold\b will not insert a newline "
+		"decremented by one.  \bfold\b will not insert a newline "
 		"immediately before or after a backspace.]"
 	"[+tab?Each tab character encountered will advance the column "
 		"position to the next tab stop.  Tab stops are at each "

src/lib/libcmd/join.c

@@ -478,7 +478,7 @@ outfield(Join_t* jp, int index, register int n, int last)
 		{
 			register unsigned char*	sp = jp->state;
 
-			/*eliminate leading spaces */
+			/* eliminate leading spaces */
 			if (jp->mb)
 				for (;;)
 				{

src/lib/libcmd/tail.c

@@ -48,7 +48,7 @@ static const char usage[] =
 		"[+m?1 MiB.]"
 		"[+g?1 GiB.]"
 	"}"
-"[+?For backwards compatibility, \b-\b\anumber\a  is equivalent to "
+"[+?For backwards compatibility, \b-\b\anumber\a is equivalent to "
 	"\b-n\b \anumber\a and \b+\b\anumber\a is equivalent to "
 	"\b-n -\b\anumber\a. \anumber\a may also have these option "
 	"suffixes: \bb c f g k l m r\b.]"

src/lib/libcmd/uniq.c

@@ -37,7 +37,7 @@ static const char usage[] =
 	"to standard output.  If no \ainfile\a is given, or if the \ainfile\a "
 	"is \b-\b, \buniq\b reads from standard input with the start of "
 	"the file defined as the current offset.]"
-"[c:count?Output the number of times each line occurred  along with "
+"[c:count?Output the number of times each line occurred along with "
 	"the line.]"
 "[d:repeated|duplicates?Output the first of each duplicate line.]"
 "[D:all-repeated?Output all duplicate lines as a group with an empty "