Merge pull request #499 from mike-pm/master

[MP/SP] Code maintenance
[MP] Fixed issue with ENTITYNUM_NONE.
[MP] Allow g_debugDamage cvar in all builds.
[MP] Fix a few gcc warnings in server demo code
[MP/SP] Remove unused #includes of "stringed_ingame.h"
Merge branch 'master' of https://github.com/JACoders/OpenJK