number_format bug fix

Hi, I was trying to enhance the functionality of number_format() (not finished, as I think I need to ask about changes first :-)), and happened to notice this bug while testing and saw it mentioned in a couple bug reports from almost 2 years ago, but it hasn't been fixed. Bug #29538, and it's also mentioned at the end of #28228. Where number_format(1234, 2, '', ',') returns 123,400 instead of the expected 1,23400 Happens when decimal places is > 0 with an empty decimal separator. There's a test with that criteria, but the thousands separator is also empty, which hides the bug. I was going to wait and include the fix with my proposed number_format changes, but I was thinking you may want to patch this in 4.4.3 also (just fixing the bug, since I know it doesn't get new features). I don't know the backporting "protocol" or if it's too late for 4.4.3, I just saw that Derick wants to release it this month and wanted to ask. I'll send a patch for all 3 branches if you want it, otherwise I'll just wait... Matt