Add -stack-select-frame command (MI)

Summary:
Add -stack-select-frame command + test.

All tests pass on OS X.

Reviewers: abidh, emaste, clayborg

Reviewed By: clayborg

Subscribers: lldb-commits, emaste, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D7765

llvm-svn: 229901