Push

Added an option that changes the behavior of tagging instructions in Clojush, so that they tag without popping the tagged items off of the stacks from which they came. Details below.

Available as usual from: https://github.com/lspector/Clojush

20110409: - Added support for no-pop tagging through a var called
            global-pop-when-tagging (holding an atom with a boolean value)
            and a boolean argument to pushgp called pop-when-tagging. 
            The defaults are true, for backwards compatibility. If 
            @global-pop-when-tagging is false (which will result from 
            passing false as a :pop-when-tagging keyword argument to pushgp)
            then executing instructions of the form tag_[type]_[number]
            will tag a value as usual, but the tagged item will not be popped
            from its source stack.