[RFC] CLI option parsing and usage generation for porcelains

  Following Kristian momentum, I've reworked his parse_option module
quite a lot, and now have some quite interesting features. The series is
available from git://git.madism.org/git.git (branch ph/strbuf).

  The following series is open for comments, it's not 100% ready for
inclusion IMHO, as some details may need to be sorted out first, and
that I've not re-read the patches thoroughly yet. Though I uses the tip
of that branch as my everyday git for 2 weeks or so without any
noticeable issues.

  And as examples are always easier to grok:

$ git fetch -h usage: git-fetch [options] [<repository> <refspec>...]

  -q, --quiet           be quiet
  -v, --verbose         be verbose

  -a, --append          append in .git/FETCH_HEAD
  -f, --force           force non fast-forwards updates
  --no-tags             don't follow tags at all
  -t, --tags            fetch all tags
  --depth <depth>       deepen history of a shallow clone

Advanced Options
  -k, --keep            keep downloaded pack
  -u, --update-head-ok  allow to update the head in the current branch
  --upload-pack <path>  path to git-upload-pack on the remote

$ git rm -rf xdiff # yeah -rf now works ! rm 'xdiff/xdiff.h' rm 'xdiff/xdiffi.c' rm 'xdiff/xdiffi.h' rm 'xdiff/xemit.c' rm 'xdiff/xemit.h' rm 'xdiff/xinclude.h' rm 'xdiff/xmacros.h' rm 'xdiff/xmerge.c' rm 'xdiff/xprepare.c' rm 'xdiff/xprepare.h' rm 'xdiff/xtypes.h' rm 'xdiff/xutils.c' rm 'xdiff/xutils.h'