Support escapes and quotes in string and character values.

Summary:
Escape characters in strings and strings containing quotes were not appearing correctly in expression values.

Patch from paulmay@microsoft.com

Reviewers: abidh, ChuckR, paulmaybee

Subscribers: greggm, lldb-commits

Differential Revision: http://reviews.llvm.org/D11371

llvm-svn: 243383