git-cvsexportcommit can't commit files which have been removed from CVS

git-cvsexportcommit can't commit files which have been removed from CVS

If a file X is removed from CVS, it goes into the Attic directory, and CVS
reports it as 'no file X' but with status 'Up-to-date'.  cvsexportcommit
misinterprets this as an existing file and tries to commit a file with the
same name.  Correctly identify these files, so that new files with the
same name can be committed.

Add a test to t9200-git-cvsexportcommit.sh, which tests that we can
re-commit a removed filename which remains in CVS's attic. This adds a
file 'attic_gremlin' in CVS, then "removes" it, then tries to commit a
file with the same name from git.

Signed-off-by: Nick Woolley <git.wu-lee@noodlefactory.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>