This fixes crashes in the menus.

Fix OpenGL "color bug"

See merge request STJr/SRB2!795

Fix R_CacheRotSprite not working with PNG lumps

See merge request STJr/SRB2!800

Fix seenames not working without a SeenPlayer hook

See merge request STJr/SRB2!799

Clear setrenderneeded after calling VID_CheckRenderer

See merge request STJr/SRB2!793

Fix the issue !678 did, but just don't exit if the file was added twice

See merge request STJr/SRB2!753

M_Ftrim

See merge request STJr/SRB2!798

- Use '%f' instead of '%g' to avoid going scientific. Should also fix some
  compiler warnings.
- The trailing zero trimming code is now useful. It started on the terminating
  byte before and wouldn't have done anything with '%g' anyway.
- Use the absolute fractional value to avoid a sign.

"+" command line parameters make sense

See merge request STJr/SRB2!707

Trim the trailing zeros off floats for cvars

See merge request STJr/SRB2!716

Local Color Table for GIF movie mode

See merge request !742

Don't freeslot TOL_ twice

See merge request STJr/SRB2!779

Allow models for skin/sprites with same name

See merge request STJr/SRB2!767

No more console in menus because codebase sucks xd

See merge request !791

This reverts commit ef3d462e.

Fix object shadow not appearing for mid-joiners

See merge request STJr/SRB2Internal!627

Fix dedicated servers not running gamelogic

See merge request STJr/SRB2!788

Note to future testers:
Remember to test dedicated servers before merging.
And splitscreen also.