Small release.
- pthread.py: fixes for paranoid C warnings-as-errors options
- gitversion.py: it now sets GIT_BRANCH with current git branch
- subproject.py: add workaround for configuration with absolute path
- strip_on_install.py: strip and objdump are optional now
- sdl2.py: sdl2-config fallback for pkg-config
- conan.py is removed due to disinterest of supporting it
- upgrade to Waf 2.0.27
- Waf's gccdeps.py and msvcdeps.py are enabled by default