-Add: Optional recursive locking of mutexes.

git-svn-id: http://svn.openttd.org/trunk@26349 6aa0318a-3be1-0310-93fa-89fd2396df07
-Fix (r26349): Silly bugs are silly.

git-svn-id: http://svn.openttd.org/trunk@26350 6aa0318a-3be1-0310-93fa-89fd2396df07
-Fix: Protect all VideoDriver_SDL methods with the _draw_mutex.

git-svn-id: http://svn.openttd.org/trunk@26351 6aa0318a-3be1-0310-93fa-89fd2396df07