Add MutableObjectId setByte to modify a mutable id

This mirrors the getByte() API in ObjectId and allows the caller to
modify a single byte, which is useful when updating it as part of a
loop walking through 0x00..0xff inside of a range of objects.

Change-Id: I57fa8420011fe5ed5fc6bfeb26f87a02b3197dab
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
2 files changed