Make filename easy to override

Author: HD Moore

lib/msf/core/exploit/fileformat.rb

@@ -26,8 +26,12 @@ def initialize(info = {})
 		)
 	end
 
+	def file_format_filename
+		datastore['FILENAME']
+	end
+
 	def file_create(data)
-		fname = datastore['FILENAME']
+		fname = file_format_filename
 		ltype = "exploit.fileformat.#{self.shortname}"
 		full_path = store_local(ltype, nil, data, fname)
 		print_good "#{fname} stored at #{full_path}"