clang-format: Initial support for try-catch.

Most of this patch was created by Alexander Rojas in
http://reviews.llvm.org/D2555
Thank you!

Synced and addressed review comments.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208302 91177308-0d34-0410-b5e6-96231b3b80d8