Merge branch 'jk/bundle-use-dash-for-stdfiles'

Merge branch 'jk/bundle-use-dash-for-stdfiles'

"git bundle" learned that "-" is a common way to say that the input
comes from the standard input and/or the output goes to the
standard output.  It used to work only for output and only from the
root level of the working tree.

* jk/bundle-use-dash-for-stdfiles:
  parse-options: use prefix_filename_except_for_dash() helper
  parse-options: consistently allocate memory in fix_filename()
  bundle: don't blindly apply prefix_filename() to "-"
  bundle: document handling of "-" as stdin
  bundle: let "-" mean stdin for reading operations