fix detection for CXX=clang
travis: for now, clang build result should not impact overall build result
hopefully this gives us just two travis builds (not 4)
build-mg.sh: no more warning when clang is not installed [ci skip]
travis: don't apt-get upgrade build node
Windows: delete Release\*.tlog before building
No prompt for file removal
Also support -DCMAKE_BUILD_TYPE=None which is used by Debian

Fixes: https://bugs.debian.org/739068
Merge pull request #9 from pabs3/develop

Also support -DCMAKE_BUILD_TYPE=None which is used by Debian
Disabled button in lobby which holds players name.