added an option to adjust the alpha clipping value in the oprnGL preferenes. in some cases you might

want to use 0.5 to see through more of the texture. (less halo's with clipmaps), defailt is 0.0 so it 
will only clip 0 alpha.

source/blender/src/space.c

@@ -3865,8 +3865,13 @@ void drawinfospace(ScrArea *sa, void *spacedata)
 			&(U.uiflag), 0, 0, 0, 0, "Hide files/datablocks that start with a dot(.*)");
 
 		uiDefBut(block, LABEL,0,"OpenGL:",
-			(xpos+edgsp+(5*midsp)+(5*mpref)),y6label,mpref,buth,
+			(xpos+edgsp+(5*midsp)+(5*mpref)),y7label,mpref,buth,
 			0, 0, 0, 0, 0, "");
+		
+		uiDefButF(block, NUMSLI, B_DRAWINFO, "Clip Alpha: ",
+				  (xpos+edgsp+(5*mpref)+(5*midsp)),y6,mpref,buth,
+				   &(U.glalphaclip), 0.0, 1.0, 0, 0, "Clip alpha below this threshold in the 3d textured view");
+		
 		uiDefButBitI(block, TOGN, USER_DISABLE_MIPMAP, B_MIPMAPCHANGED, "Mipmaps",
 			(xpos+edgsp+(5*mpref)+(5*midsp)),y5,mpref,buth,
 			&(U.gameflags), 0, 0, 0, 0, "Toggles between mipmap textures on (beautiful) and off (fast)");