Stub out system functions for testing (WIP).

Stub out system functions for testing (WIP).

This is a more thorough and should be an overall better approach than
stubbing/mocking the base_proc_service class itself.

This commit introduces a baseproc-sys.h header which holds aliases for
the system functions that are used (kill, fcntl, etc). When running
tests the functions will be mocked (currently they are rigged to abort
when called).