Document how git-p4 currently works when specifying multiple
depot paths:
1. No branches or directories are named.
2. Conflicting files are silently ignored---the last change
wins.
2. Option --destination is required, else the last path is construed
to be a directory.
3. Revision specifiers must be the same on all paths for them to
take effect.
Test this behavior.
Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>