in the AMD case, reveal the global right away

This is to accomodate synchronous code that might be running alongside
AMD modules.  The AMD case already exposes the window.Raven global,
however previous to this patch it waited until the AMD module was
specified as a dependency before initializing the global.
Merge pull request #288 from mwcz/reveal-global-when-amd

in the AMD case, reveal the global right away