Cannot cherry pick a merge commit

When attempting to cherry pick a merge commit, the command fails because there is no -m option specified (mainline parent number).

Though it may not be possible to automatically determine the mainline parent for a merge commit, perhaps allowing the user to simply select the mainline from one of the parents of the merge commit may suffice.

I think the only other place where this issue should arise is when performing a revert of a merge commit, and there is already a ticket for that issue (SRCTREEWIN-593)