Cleaning up the self initialization checker.

-Allow Sema to do more processing on the initial Expr before checking it.
-Remove the special conditions in HandleExpr()
-Move the code so that only one call site is needed.
-Removed the function from Sema and only call it locally.
-Warn on potentially evaluated reference variables, not just casts to r-values.
-Update tests.

llvm-svn: 164951