Add -k option to cvsexportcommit to revert expanded CVS keywords in CVS working tree...

Add -k option to cvsexportcommit to revert expanded CVS keywords in CVS working tree before applying commit patch

Depending on how your CVS->GIT conversion went you will have some
unexpanded CVS keywords in your GIT repo. If any of your git commits
touch these lines then the patch application will fail. This patch
addresses that by adding an option that will revert and expanded CVS
keywords to files in the working CVS directory that are affected by
the commit being applied.

Signed-off-by: Alex Bennée <alex@bennee.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>