Log Message:
Update waf to 1.8.20:

NEW IN WAF 1.8.20
-----------------
* Detection SUN cc compiler version 5.0 #1697
* Initialize 'VALAFLAGS' with OS flags #1703
* Convert --perlbinary data to list #1705
* Cppcheck fixes #1708
* Boost module enhancements and fixes #1709
* Various cpplint enhancements #1711
* Workaround for unreadable home folders