Finished themes for transparent Button regions in Blender.

Notes and image:
http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.66/Usability

- now each editor has own settings for "show panel header" and
  "show panel background", and colors+alpha for this.

- this setting used to be global for all editors, but it can conflict
  with looks of specific editors. 

- Now you can set for editors to show panels with a 100% transparent
  tool/properties region. 

Note: read XML theme files now might get an error, Campbell will fix.

source/blender/editors/space_file/space_file.c

@@ -533,7 +533,7 @@ static void file_ui_area_draw(const bContext *C, ARegion *ar)
 {
 	float col[3];
 	/* clear */
-	UI_GetThemeColor3fv(TH_PANEL, col);
+	UI_GetThemeColor3fv(TH_BACK, col);
 	glClearColor(col[0], col[1], col[2], 0.0);
 	glClear(GL_COLOR_BUFFER_BIT);