Use more robust minifer than JSMin (with a real parser)

[westonruter]

BeHeard reported an issue on the WP forums, whereby dependency minification was failing on one or more scripts. The specific error was (see screenshot at end of description):

JSMin: Unterminated RegExp at byte 230500: /g,"%2D%2D")+ Try again

It looks like a bug in JSMin, cause by the fact that it is not use a real parser: https://code.google.com/p/minify/issues/detail?id=222

So we should by default use JSMinPlus, and then fallback to JSMin, and if that does not work, throw the error described in #18. Note that I had defailed to JSMin since JSMinPlus was also failing to minify some script I was using during testing. We could use Google's Closure Compiler, but then we have to break up the code into chunks since Google imposes a limit on the POST size.

[westonruter]

Duplicate of #7