Correctly find refPkg when project is within a node_modules folder
Correctly find refPkg when project is within a node_modules folder

If a project is running from within a node_modules folder the
`System.baseURL` will contain the string "node_modules". When looking up
the refPkg we detect this by looking for "node_modules". We really want
to know if we are within the *project's* own node_modules folder.

Closes #149

stealjs/system-npm,stealjs/system-npm,stealjs/steal-npm,stealjs/steal-npm