Correct a few types to be unsigned in fast-import.
Correct a few types to be unsigned in fast-import.

The length of an atom string cannot be negative.  So make it
explicit and declare it as an unsigned value.

The shift width in a mark table node also cannot be negative.
I'm also moving it to after the pointer arrays to prevent any
possible alignment problems on a 64 bit system.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

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