Issue #18037: Do not escape '\u' and '\U' in raw strings.
Closes #13867: remove untrue comment about PyWeakref_Check().
Fix wrong link.
Minor grammar fix.
Issue 19158:  a rare race in BoundedSemaphore could allow .release() too often.
(grafted from e06edc0c7a4951327f0c95ebeebccba6879a6063)
LOL - 2.7 requires very different code.  Annoying ;-)