Rename unwind_diagnose.py to diagnose_unwind.py.  Change
finish-swig-Python-LLDB.sh to create a new lldb.diagnose subdirectory
in the LLDB framework; the first diagnostic command in this directory
is diagnose-unwind.  There may be others added in the future.

Users can load these diagnostic tools into their session with
"script import lldb.diagnose".