swift234

Variables in 'case' labels with multiple patterns.

Parser now accepts multiple patterns in switch cases that contain variables.
Every pattern must contain the same variable names, but can be in arbitrary
positions. New error for variable that doesn't exist in all patterns.

Sema now checks cases with multiple patterns that each occurence of a variable
name is bound to the same type. New error for unexpected types.

SILGen now shares basic blocks for switch cases that contain multiple
patterns. That BB takes incoming arguments from each applicable pattern match
emission with the specific var decls for the pattern that matched.

Added tests for all three of these, and some simple IDE completion
sanity tests.