Merge branch 'nd/dwim-wildcards-as-pathspecs' into maint

"git show 'HEAD:Foo[BAR]Baz'" did not interpret the argument as a
rev, i.e. the object named by the the pathname with wildcard
characters in a tree object.

* nd/dwim-wildcards-as-pathspecs:
  get_sha1: don't die() on bogus search strings
  check_filename: tighten dwim-wildcard ambiguity
  checkout: reorder check_filename conditional