LibClang for llvm-3.4 & rtags-rename-symbol

Two trivial changes:

1. add an additional libclang path for llvm debian/Ubuntu nightly,
http://llvm.org/apt/
in this case index.h is in /usr/lib/llvm-3.4/include/clang-c/ rather
than the canonical one

2. an additional save buffer operation is added after
rtags-rename-symbol

Really minor changes and I just would like to try github's pull request functionality:-)
BTW, there must be a *much* better way to for buffer saving for rtags-rename-symbol.