Make one-way recolors check for specific files

So, 2.3 added recoloring one-way tiles to no longer make them be always
yellow. However, custom levels that retexture the one-way tiles might
not want them to be recolored. So, if there are ANY custom assets
mounted, then the one-ways will not be recolored. However, if the XML
has a <onewaycol_override>1</onewaycol_override> tag, then the one-way
will be recolored again anyways.

When I added one-way recoloring, I didn't intend for any custom asset to
disable the recoloring; I only did it because I couldn't find a way to
check if a specific file was customized by the custom level or not.

However, I have figured out how to do so, and so now tiles.png one-way
recolors will only be disabled if there's a custom tiles.png, and
tiles2.png one-way recolors will only be disabled if there's a custom
tiles2.png.

In order to make sure we're not calling PhysFS functions on every single
deltaframe, I've added caching variables, tiles1_mounted and
tiles2_mounted, to Graphics; these get assigned every time
reloadresources() is called.

desktop_version/src/Graphics.h

@@ -162,7 +162,7 @@ public:
 	void drawbackground(int t);
 	void updatebackground(int t);
 #ifndef NO_CUSTOM_LEVELS
-	bool shouldrecoloroneway(const int tilenum);
+	bool shouldrecoloroneway(const int tilenum, const bool mounted);
 #endif
 	void drawtile3( int x, int y, int t, int off, int height_subtract = 0 );
 	void drawtile2( int x, int y, int t );
@@ -187,6 +187,10 @@ public:
 	bool onscreen(int t);
 
 	void reloadresources(void);
+#ifndef NO_CUSTOM_LEVELS
+	bool tiles1_mounted;
+	bool tiles2_mounted;
+#endif
 
 
 	void menuoffrender(void);