Make changePage working properly on PhoneGap with WP7

WP7 with PhoneGap uses different local file name which has form like:
x-wmapp1:/app/www/index.html
Currently navigation helper assumes that every URL has double slash in url which is not the case in this situation. I added fix which always checks if there is double slash necessary for given url. That makes this working for all tradtional urls, as well as for WP7.