Fixes in the IRInterpreter:

- removed an unnecessary variable
- fixed an issue where we sometimes
  wrote too much data into a buffer
- made the recognition of variables
  as "this" a little more conservative

<rdar://problem/13216268>


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@175318 91177308-0d34-0410-b5e6-96231b3b80d8