zip / unzip need ironruby support

[mxriverlynn]

currently there are no zip gems for ruby that will run in ironruby (none that i know of, anyways...). need to do something to get zip / unzip tasks working in ironruby.

ben hall had a good idea:

dynamicaly require files based on runtime. the required file is a facade over a specific zip / unzip implementation - either for standard ruby zip gem, or for ironruby intertop to a c# zip library.

[mxriverlynn]

recently added a IS_IRONRUBY flag to the specs, so i could use System.XML to validate some xml output for the nuspec task. should be able to use the same idea and create an ironruby compatible zip task using one of the open source zip libs for .net