'usage: merge <string:mode> <image:pic1>
[<image:pic2> [<image:pic3> [<image:pic4>]]]
Merge top-of stack images in a way described by the mode.'

def do_merge(self):

    mode = self.do_pop()
    bandlist = []
    for band in mode:
        bandlist.append(self.do_pop())
    self.push(Image.merge(mode, bandlist))
