NWN: Properly initialize ScriptFunctions::_module

Fixes Coverity issue #1248131.
NWN: Properly initialize CharGenBase::CharacterAbilities::race

Fixes Coverity issues #1248133 and #1248132.
SOUND: Properly delete[] memory when decodeFrame() fails

Fixes Coverity issue #1038247.
BUILD: Compile with 4 jobs

The Travis documentation says that this might speed up the
build process, even though the VM runs with only 1.5 cores.
GRAPHICS: Correct validation conditional.
BUILD: Set up Travis CI / Coverity Scan integration