swift234

Fix: <rdar://problem/16230507> Cannot use a negative constant as the second operator of ... operator

This is a case that the operator splitting code didn't handle because of
the bizarre lexer code for handling operators with periods in them.  We had
accreted some weird special case logic for what is valid in an operator
(but which even had a special case hack for ..<).  The policy is now very
simple: if an operator name starts with a dot, it is allowed to include other
dots in its name.  If it doesn't, it doesn't.  This allows us to get lexer
level operator splitting in cases like x=.Foo, allowing our existing operator
set that have dots in them without hacks, and provides a superior QoI
experience due to operator splitting.

This is technically a language change, but the TSPL operator grammar was
incorrect for it anyway.  I will file an internal radar to get TSPL updated
with the actual behavior (now that it is defensible).