pathspec: avoid the need of "--" when wildcard is used

When "--" is lacking from the command line and a command can take both revs and paths, the idea is if an argument can be seen as both an extended SHA-1 and a path, then "--" is required or git refuses to continue. It's currently implemented as: (1) if an argument is rev, then it must not exist in worktree (2) else, it must exist in worktree (3) else, "--" is required. These rules work for literal paths, but when non-literal pathspec is involved, it almost always requires the user to add "--" because it fails (2) and (1) is really rarely met (take "*.c" for example, (1) is met if there is a ref named "*.c"). This patch modifies the rules a bit by considering any valid (*) wildcard pathspec "exist in worktree". The rules become: (1) if an arg is a rev, then it must either exist in worktree or not be a valid wildcard pathspec. (2) else, it either exists in worktree or is a wildcard pathspec (3) else, "--" is required. With the new rules, "--" is not needed most of the time when wildcard pathspec is involved. Signed-off-by: Junio C Hamano <gitster@pobox.com>