Apparently we did not copy the blob SHA1 into the stack variable
'sha1' when a mark is used to refer to a prior blob. This code
was not previously tested as the Mozilla CVS -> git-fast-import
program always fed us full SHA1s for modified blobs and did not
use the mark feature there.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>