More robust race condition prevention.

As discussed in issue #35 there is a potential problem on gpm install where some dependency of the packages we install through go get , this happens because gpm installs all packages in parallel for performance reasons.

This version will be marked as a pre-release, we are attempting to solve this problem without having to cut out parallel package installation from the codebase, as that makes gpm quite a bit slower. My plan is to wait for one or two weeks and determine if this patch is the way to go or if we should sacrifice performance to make the tool more robust.

If you have any thoughts or comments about this problem or fix please add them to the issue!.

Keep on goph'in!