Message 83363 - Python tracker

I've hit this, too, and it's annoyed me. So here's a patch against trunk
that should fix it. 

The idea is: whenever unicode_literals are turned on (or the -U command
line flag is passed), to convert r"\u" to "\u005c\u0075" and r"\U" to
"\u005c\u0055" for every string literal in the source file before
passing the string to PyUnicode_DecodeRawUnicodeEscape.