Fixes bug with loading npm modules

Fixes bug with loading npm modules if relative path is used in package.json.
For example see this part of package.json:
{ 
...
"main": "./moment.js",
... 
}

commonjs bridge will try to match it with loaded file in the following line:
if (existingfiles[paths[i]]) {
and fail since paths[i] will be smth like 
basepath/node_modules/moment/moment/./moment.js 
but in existing files it will be 
basepath/node_modules/moment/moment/moment.js