Fixes for -G/--globstar (re: 5312a59d)

The fix for '.' and '..' in regular globbing broke '.' and '..' in
globstar. No globstar pattern that contains '.' or '..' as any
pathname component still matched. This commit fixes that.

This commit also makes symlink/** mostly work, which it never has
done in any ksh93 version. It is correct and expected that symlinks
found by patterns are not resolved, but symlinks were not resolved
even when specified as explicit non-pattern pathname components.
For example, /tmp/** breaks if /tmp is a symlink (e.g. on macOS),
which looks like a bug.

src/lib/libast/include/glob.h,
src/lib/libast/misc/glob.c: glob_dir():
- Make symlink/** work. we can check if the string pointed to by
  pat is exactly equal to *. If so, we are doing regular globbing
  for that particular pathname element, and it's okay to resolve
  symlinks. If not (if it's **), we're doing globstar and we should
  not be matching symlinks.
- Let's also introduce proper identification of symlinks (GLOB_SYM)
  and not lump them in with other special files (GLOB_DEV).
- Fix the bug with literal '.' and '..' components in globstar
  patterns. In preceding code, the matchdir pointer gets set to the
  complete glob pattern if we're doing globstar for the current
  pathname element, null if not. The pat pointer gets set to the
  elements of the pattern that are still left to be processed;
  already-done elements are trimmed from it by increasing the
  pointer. So, to do the right thing, we need to make sure that '.'
  or '..' is skipped if, and only if, it is the final element in
  the pattern (i.e., if pat does not contain a slash) and is not
  specified literally as '.' or '..', i.e., only if '.' or '..' was
  actually resolved from a glob pattern. After this change,
  '**/.*', '**/../.*', etc. do the right thing, showing all your
  hidden files and directories without undesirable '.' and '..'
  results; '.' and '..' are skipped as final elements, unless you
  literally specify '**/.', '**/..', '**/foo/bar/..', etc.

src/cmd/ksh93/COMPATIBILITY:
- Note the symlink/** globstar change.

src/cmd/ksh93/sh.1:
- Try to document the current globstar behaviour more exhausively.

src/cmd/ksh93/tests/glob.sh:
- Add tests. Try to cover all the corner cases.

src/cmd/ksh93/tests/shtests:
- Since tests in glob.sh do not use err_exit, they were not
  counted. Special-case glob.sh for counting the tests: count the
  lines starting with a test_* function call.

Resolves: https://github.com/ksh93/ksh/issues/146

src/cmd/ksh93/sh.1

@@ -6942,13 +6942,37 @@ Requires
 to truncate a file when turned on.
 .TP 8
 .B \-G
-Causes the pattern
+Enables recursive file name generation.
+This adds the double-star pattern
 .B **
-by itself to match files and zero or more directories and sub-directories
-when used for file name generation.
-If followed by a
-.B /
-only directories and sub-directories are matched.
+to the file generation mechanism (see
+.I "File Name Generation\^"
+above).
+By itself, it matches the recursive contents of the current directory,
+which is to say, all files and directories in the current directory
+and in all its subdirectories, sub-subdirectories, and so on.
+If the pathname pattern ends in
+.BR **/ ,
+only directories and subdirectories are matched,
+including symbolic links that point to directories.
+A prefixed directory name is not included in the results unless that
+directory was itself found by a pattern. For example,
+.B dir/**
+matches the recursive contents of
+.B dir
+but not
+.B dir
+itself, whereas
+.B di[r]/**
+matches both
+.B dir
+itself and the recursive contents of
+.BR dir .
+Symbolic links to non-directories are not followed.
+Symbolic links to directories are followed if they are specified literally
+or match a pattern as described under
+.IR "File Name Generation\^" ,
+but not if they result from a double-star pattern.
 .TP 8
 .B \-H
 Enable \f3!\fP-style history expansion similar to