Clear old camera from previous level

The sound code could accidentally reference an old invalid camera during
level spawn
Merge remote-tracking branch 'upstream/master'
Player prediction fixes in PIT_CheckThing

Player prediction could end up executing functions for TOUCHY things or
modify velocities when BLASTED, among other things.
Fix two issues with GL nodes handling

Fix inability to load GL nodes for maps with names longer than 5 characters.
Fix inability to load GL nodes from external GWA files.