add gperftools (tcmalloc and friends)
Allow fake installations (just make the directory).

- Use for debugging.
Fix for SPACK-49.

- name conflict in imp.load_source caused this to fail.
- Python modules loaded by imp have unique names now.
Merge branch 'bugfix/load-hooks-fix' into develop
Fix for SPACK-50

Bad format string in version check.
Merge branch 'features/gperftools' into develop