Compdb improvements

[shuber2]

I have added a couple of improvements to the compilation database python code:

• Replace regular expressions by os.path utils
• Try harder to find correct entry in database, e.g., when header file is not in same directory as implementation file.
• Also recognize -std compilation options, e.g., in my case -std=c++11.
• Rename complete_database.py to compilation_database.py, which is a better name.