Fix undefined totalWeight value crash.

Happens after the map is loaded.
cgame: change cgs.mapname to 'maps/_.bsp' to '_'
renderers: add ScissorSet and ScissorEnable

Used to control temporarily glScissor, the scissor is also modified
by other parts of the renderer.
Adapted from a commit from `Ishq (ded55d8f12e03aceff) + fixes
cgame: Add scissoring support
Fix quoting of some adminhelp output.
Don't abort map loading in the presence of a second worldspawn.

Report the error anyway; don't retain the offending entity.
(Fixes loading of veddak-final.)
Change order of includes to prevent errors
Merge remote-tracking branch 'remotes/origin/master' into bots