Fix expression evaluation with operator new

Summary:
referencing a user-defined operator new was triggering an assert in clang because we were
registering the function name as string "operator new", instead of using the special operator
enum, which clang has for this purpose. Method operators already had code to handle this, and now
I extend this to cover free standing operator functions as well. Test included.

Reviewers: spyffe

Subscribers: sivachandra, paulherman, lldb-commits

Differential Revision: http://reviews.llvm.org/D17856

llvm-svn: 278670