I'm also wondering about the case of simple pull requests... What are the requirements to send some and it being accepted?
Make a successful thread about it in dev/tech discussion? Make theymos/Gavin/etc agreeing with you? Nothing? Luck? Prayers to Satoshi?
No formal requirements, no formal process (that I've seen).
Make the pull request, people will see it, comment, etc. If there are no big objections and at least a couple of ACKs, it'll get pulled. Most of the discussion happens on the github page and in IRC. Try to make sure your branch is correct and complete before you make the request. If your patch is not totally trivial, you'll need to make some changes before it'll be accepted, but it looks bad when the build tester bot reports that your pullreq can't compile.
As for the two specific examples in this thread, I like the -purgetransaction option. Personally, I'd prefer an RPC call that selectively removes one transaction without needing a restart, but this would still come in handy at times. As for the source for sendmany, can't you just specify the default account with an empty string "" ?