post install tasks requiring node fail, when using 2.x npm version

with npm 2.0 a breaking change was introduced to how the npm scripts are handled:

https://github.com/npm/npm/commit/021770b9cb07451509f0a44afff6c106311d8cf6

this change does not add the node executable directory of the current process when executing npm scripts. some modules, like karma phantomjs launcher, rely on executing node commands as part of the post install scripts. this post install scripts will fail on machines without global node installation