Misc code cleanups, little SkeletalSprite loading improvement.

- Removed some unused member variables.

- The BBGE_BUILD_WIDESCREEN define is now gone.

- Added an TiXMLDocument cache to prevent parsing the same file
once for each entity on the map with the same skeletal.

- Removed Lua func entity_warpToPathStart, which was essentially a no-op
because Entity::followingPath was always NULL. Removed related code.

- Set texture wrap only when required.

(Some changes taken from https://bitbucket.org/mattbierner/ios-aquaria,
special thanks for changeset 72d6460d9e60)

Aquaria/DSQ.cpp

@@ -1057,11 +1057,7 @@ This build is not yet final, and as such there are a couple things lacking. They
 
 	debugLog("Init Graphics Library...");
 		initGraphicsLibrary(user.video.resx, user.video.resy, fullscreen, user.video.vsync, user.video.bits);
-#ifdef BBGE_BUILD_WIDESCREEN
 		core->enable2DWide(user.video.resx, user.video.resy);
-#else
-		core->enable2D(800, 600, 1);
-#endif
 		core->initFrameBuffer();
 	debugLog("OK");
 
@@ -2245,6 +2241,7 @@ void DSQ::shutdown()
 
 	core->particleManager->clearParticleBank();
 	Shot::clearShotBank();
+	SkeletalSprite::clearCache();
 
 
 	cursor->setTexturePointer(0, RenderObject::NO_ADD_REF);