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)

BBGE/ByteBuffer.h

@@ -102,7 +102,7 @@ public:
 	sprintf(errbuf, "Exception in ByteBuffer: '%s', rpos: %u, wpos: %u, cursize: %u, sizeparam: %u", \
 	__e.action, __e.rpos, __e.wpos, __e.cursize, __e.sizeparam); errorLog(errbuf); abort(); }
 #else
-#define BYTEBUFFER_EXCEPT(bb, desc, sz) throw ByteBufferException(bb, desc, sz)
+#define BYTEBUFFER_EXCEPT(bb, desc, sz) throw Exception(bb, desc, sz)
 #endif
 
 protected: