Moved most uses of glGetTexImage() into a single function with better error checking.

Also small config addition to optionally increase memory allocation size
for temporary texture pixel data; the nouveau drivers seem notoriously
awkward and keep writing over the buffer.

BBGE/Texture.h

@@ -80,6 +80,10 @@ public:
 
 	void write(int tx, int ty, int w, int h, const unsigned char *pixels);
 	void read(int tx, int ty, int w, int h, unsigned char *pixels);
+
+	unsigned char *getBufferAndSize(int *w, int *h, unsigned int *size); // returned memory must be free()'d
+	static int textureMemoryMultiplier; // 1. More for buggy drivers.
+
 protected:
 	std::string loadName;