1) Fixed a bug where XQUARTZ was #defined when auto but not when --enable-xquartz
2) Cleaned up missing #includes and function prototypes.
3) Fixed some invalid C syntax problems
4) Removed a bunch of dead code
5) Cleaned up code to prevent some warnings
6) Bugfix in xpr/x-hook.c - looks like someone just forgot to finish writing code for hook_remove()... I only noticed it because gcc -Wall complained about reaching the end of a non-void function... lucky for us gcc is smarter than we are.
