This the first part for improving source location fidelity for types,
changes to follow:
-The Parser will not create any types, it will just create TypeReprs.
-The type checker will create the types by going through TypeReprs.
-IdentifierType will be removed.
Swift SVN r6112
A single case block can have one or more 'case ...:' labels. 'case' labels contain patterns instead of exprs. 'default:' is a funny spelling for 'case _:'. Change the CaseStmt representation and rip out all the parsing, type-checking, and SILGen built off the old representation.
Swift SVN r5795