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/cmd/ksh93/include/nval.h

@@ -88,7 +88,7 @@ struct Namarray
 	void	*(*fun)(Namval_t*,const char*,int);	/* associative arrays */
 	void		*fixed;			/* for fixed sized arrays */
 	Dt_t		*table;			/* for subscripts */
-	void		*scope;			/* non-zerp when scoped */
+	void		*scope;			/* non-zero when scoped */
 };
 
 /* The context pointer for declaration command */
@@ -167,7 +167,7 @@ struct Namval
 #define NV_HEXFLOAT	(NV_LTOU)	/* for C99 base16 float notation */
 #define NV_FLTSIZEZERO	-1		/* a float with size of 0 being <0 */
 
-/*  options for nv_open */
+/* options for nv_open */
 
 #define NV_APPEND	0x10000		/* append value */
 #define NV_MOVE		0x8000000	/* for use with nv_clone */
@@ -231,7 +231,7 @@ struct Namval
 #define ARRAY_UNDEF	(4L<<ARRAY_BITS)	/* For ${array} */
 
 
-/* These  are disciplines provided by the library for use with nv_discfun */
+/* These are disciplines provided by the library for use with nv_discfun */
 #define NV_DCADD	0	/* used to add named disciplines */
 #define NV_DCRESTRICT	1	/* variable that are restricted in rsh */
 
@@ -242,7 +242,7 @@ struct Namval
 #	define extern __IMPORT__
 #   endif /* _BLD_shell */
 #endif /* _DLL */
-/* prototype for array interface*/
+/* prototype for array interface */
 extern Namarr_t	*nv_arrayptr(Namval_t*);
 extern Namarr_t	*nv_setarray(Namval_t*,void*(*)(Namval_t*,const char*,int));
 extern int	nv_arraynsub(Namarr_t*);
@@ -285,7 +285,7 @@ extern void 		nv_setvec(Namval_t*,int,int,char*[]);
 extern void		nv_setvtree(Namval_t*);
 extern int 		nv_setsize(Namval_t*,int);
 extern Namfun_t		*nv_disc(Namval_t*,Namfun_t*,int);
-extern void 		nv_unset(Namval_t*);	 /*obsolete */
+extern void 		nv_unset(Namval_t*);	 /* obsolete */
 extern void 		_nv_unset(Namval_t*,int);
 extern Namval_t		*nv_search(const char *, Dt_t*, int);
 extern char		*nv_name(Namval_t*);