About the GIMP_STOCK_RESET issue.
GIMP_STOCK_RESET is used to define the ‘RESET’ button, and is a pre-defined macro in GIMP API
(as described here : GimpStock).
I have absolutely no idea why this doesn’t work anymore. Maybe the GIMP developers have done something lately and removed it ? I think this could be asked on the gimpdev mailing list eventually.