Log Message:
waf: update to 2.0.4.

NEW IN WAF 2.0.4
----------------
* Enable more advanced warnings of ant_glob on build folders in verbose mode
* Defer node.ant_glob(..., generator=True) evaluation
* Enable 'waf clean' to get the list of files to remove from bld.clean_files
* Define the environment variable WAF_NO_PREFORK to skip pre-forking
* Fix Can't pickle local object '_createenviron.<locals>.encode' \ 
exceptions (Python 3.6)
* Improve the Erlang module #2095
* Add task target to parallel_debug outputs #2091

NEW IN WAF 2.0.3
----------------
* Enable install_path=None for Python targets #2087
* Skip empty or duplicates in java user classpath #2084
* Change the unit test summary color scheme to use green and red colors
* Improve the deadlock error message
* Report sys.path values from Context.load_tool to improve error messages
* Cache qrc uic->h conversions to enable qrc re-use across targets
* Output long-running tasks outputs immediately using bld(rule=..., stdout=None)