* Added a new RNA subtype, PROP_IMAGEPATH. It's the same as PROP_FILEPATH, but for images only.

* Changed UI code to display image browser for PROP_IMAGEPATH
* Set the icon_filepath RNA property for brushes to use PROP_IMAGEPATH
* Changed preview icon drawing to ignore unset icons
* Fixed const warnings in brush RNA

source/blender/python/intern/bpy_props.c

@@ -41,6 +41,7 @@ EnumPropertyItem property_subtype_string_items[] = {
 	{PROP_FILEPATH, "FILE_PATH", 0, "File Path", ""},
 	{PROP_DIRPATH, "DIR_PATH", 0, "Directory Path", ""},
 	{PROP_FILENAME, "FILENAME", 0, "Filename", ""},
+	{PROP_IMAGEPATH, "IMAGE_PATH", 0, "Image Path", ""},
 
 	{PROP_NONE, "NONE", 0, "None", ""},
 	{0, NULL, 0, NULL, NULL}};