PATCH: Allow format-patch to attach patches

The --attach patch to git-format-patch to attach patches instead of 
inlining them.  Some mailers linewrap inlined patches (eg. Mozilla).

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  git-format-patch.sh |   52 
++++++++++++++++++++++++++++++++++++++++++++-------
  1 files changed, 45 insertions(+), 7 deletions(-)