Add write support for Fgdb layers and make it possible to remove a prefix from the expressions. The expressions returned by arcgis for Fgdb data contain the data source name as a prefix. Mapserver does not need it and does not match those expressions so they have to be removed

LAYER
	NAME "l_solid_4pt_c255-255-255"
	DATA "gewaesserlinien"
	TYPE LINE
	GROUP "line"
	STATUS ON
	METADATA
		"wms_title"                     "l_solid_4pt_c255-255-255"
	END
	CLASS
		SYMBOL "l_solid_4pt_c255-255-255"
		COLOR 0 0 0
		WIDTH 4
	END
END