New api: Envjs.getcwd

This will partially complete the transition from Envjs.uri from being a Java-based function to a near pure javascript function.

The only callout to java now is to get the "current working directory" (or getcwd in posix-land) for loading in file:// type urls.

xhr.js will have one of the following defs

// CORE.. don't really expect this to work all that well
Envjs.getcwd = function() { return "."; }

// RHINO
Envjs.getcwd = function() { return java.lang.System.getProperty("user.dir"); }

Then, I'll move the current Envjs.uri from the rhino and move into core, and have Envjs.uri use Envjs.getcwd.

I'll let this sit around as a ticket for a few days, in case anyone has an alternate idea.