Copying permissions from src to dest

hi,

I know there is already pull request #1 open for this feature, but I wanted to propose another possible solution. The idea is from [grunt-contrib-copy](https://github.com/gruntjs/grunt-contrib-copy/blob/5faf6bc64c9f6e0bd4be3fbe5335bb9885b17a82/tasks/copy.js#L58).

It would be great to get one of these pull requests (or some combination of the two) into the library to resolve logankoester/grunt-phonegap#13.

Best,
 -Eric