clib: clean up include guards in the C/C++ header files
Clean up the include guards to be more consistent and unique.
Some files used include guards like "KEY_H" and "STORE_H" which were not very
unique, and are more likely to collide with definitions provided by header
files from other projects. Some of the py-*.h files were missing include
This corresponds to Facebook diff D5588670.
Test Plan: Confirmed the code still builds and passes tests.
Reviewers: #fbhgext, quark
Reviewed By: #fbhgext, quark
Differential Revision: https://phab.mercurial-scm.org/D508