mint-arena: Use BG_NumItems() instead of bg_numItems

bg_numItems is still used in bg_misc.c
mint-arena: Move key catcher to CGame VM
Try to fix Travis CI MinGW builds

Listing i686-w64-mingw32-gcc as a compiler stopped working.
Travis tries to print version before installing it.

$ i686-w64-mingw32-gcc --version

/home/travis/build.sh: line 201: i686-w64-mingw32-gcc: command not found

The command "i686-w64-mingw32-gcc --version" failed and exited with 127 during setup.

Conflicts:
	.travis.yml
	travis-ci-build.sh
Merge remote-tracking branch 'mint-arena/master'

Conflicts:
	code/cgame/cg_ents.c
	code/game/bg_misc.c