Log Message:
waf: update to 2.0.7.

NEW IN WAF 2.0.7
----------------
* Apply priorities to dynamically-generated tasks #2137
* Fix upcoming Python 3.7 incompatibilities #2126
* Fix Python3 support in extras/xcode6.py #2121
* Improve priority support in extras/swig.py #2137
* Improve support extras/protoc.py #2135
* Improve argument handling in extras/clang_compilation_database.py #2127
* Add glib DBus bindings in extras/gdbus.py #2134
* Avoid name collisions for precompiled headers and libraries with similar names \ 
in extras/pch.py #2122