The git-cvsimport-script had a copule of small bugs that prevented me
from importing a big CVS repository.

The first was that it didn't handle removed files with a multi-digit
primary revision number.

The second was that it was asking the CVS server for "F" messages,
although they were not handled.

I also updated the documentation for that script to correspond to
actual flags.

Signed-off-by: David Kågedal <davidk@lysator.liu.se>