Merge branch 'ws/fast-export-with-revision-options'

Use of certain "git rev-list" options with "git fast-export"
created nonsense results (the worst two of which being "--reverse"
and "--invert-grep --grep=<foo>").  The use of "--first-parent" is
made to behave a bit more sensible than before.

* ws/fast-export-with-revision-options:
  fast-export: fix surprising behavior with --first-parent