git-svn: better error reporting if --follow-parent fails
git-svn: better error reporting if --follow-parent fails

This will be useful to me when I try more special-cases
of parent-tracking.

Signed-off-by: Eric Wong <8c2951295f8292b0c03727bc4652981172298eae@yhbt.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git