git-merge knows some strategies want to skip trivial merges
git-merge knows some strategies want to skip trivial merges

Most notably "ours".  Also this makes sure we do not record
duplicated parents on the parent list of the resulting commit.

This is based on Mark Wooding's work, but does not change the UI
nor introduce new flags.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

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