swift234

Start cleaning up method name importing.

Import a selector into a Swift method name, performing splitting at
that point. Use the resulting method name to determine the argument
names of the parameters, rather than trying to chop up the selector
again. There's more refactoring to do here.

This fixes a longstanding bug where the first argument of an
Objective-C method got the internal parameter name when it should
have gotten no name at all.

Swift SVN r15850