Merge branch 'misc-fixes-tomerge' into 'next'

Miscellanous fixes to merge

These are the commits from the "miscellanous-fixes" branch that are okay to merge in.

Bugs fixed include the following:
* CTF flags respawning incorrectly: they cannot z position themselves correctly, and they cannot flip themselves.
* The weird "jumping" spring/monitor effect: this is the result of an internal mobj_t pointer (tmfloorthing, specifically) not resetting itself to NULL for the next object's thinker, resulting in Z movement code thrusting the object vertically at tmfloorthing->momz.

See merge request !18