New Year's clean-up.

Throw a warning if a invalid (not present) AI is specified in a map.
Replace the last occurences of jubot with qbot.
Exclude the common siege templates from the Units Demo map.
Fix an error with flying units.
Replace CFG_GET_SYS_VAL with CFG_GET_USER_VAL and rename it to
CFG_GET_VAL to reflect its behaviour better.
Fix linker error with clang 3.2. Refs 1588.
Remove some useless includes.

This was SVN commit r13031.

source/ps/CLogger.cpp

@@ -19,7 +19,6 @@
 
 #include "CLogger.h"
 #include "CConsole.h"
-#include "ConfigDB.h"
 #include "graphics/ShaderManager.h"
 #include "graphics/TextRenderer.h"
 #include "lib/ogl.h"
@@ -48,8 +47,6 @@ static const size_t RENDER_LIMIT = 20; // maximum messages on screen at once
 
 static const size_t BUFFER_SIZE = 1024;
 
-extern int g_xres, g_yres;
-
 // Set up a default logger that throws everything away, because that's
 // better than crashing. (This is particularly useful for unit tests which
 // don't care about any log output.)