A heuristic to help the "git <cmd> <revs> <pathspec>" command line
convention to catch mistyped paths is to make sure all the non-rev
parameters in the later part of the command line are names of the
files in the working tree, but that means "git grep $str -- \*.c"
must always be disambiguated with "--", because nobody sane will
create a file whose name literally is asterisk-dot-see.  Loosen the
heuristic to declare that with a wildcard string the user likely
meant to give us a pathspec.

* nd/dwim-wildcards-as-pathspecs:
  pathspec: avoid the need of "--" when wildcard is used