make node-gyp work with io.js-nightly versions

[jakeburden]

Check process.version for 'nightly'. If using io.js nightly, the disUrl is changed accordingly, allowing for the correct tarball url path to be created.

This allows node-gyp to work in io.js nightly versions.

[rvagg]

we have next-nightly now too so this isn't quite right

I think I'm -1 on this for now since we really need to get the longer-term solution to node-gyp in there.

Some workarounds for this in the meantime are to:

1. download the source and unpack it into the correctly named subdirectory in ~.node-gyp/
2. have the source available either as an unpacked tar or the cloned repo and install/rebuild using npm and giving the flag --nodedir=/path/to/source
3. same as 2 but bake it in to your npm config with npm config set nodedir=/path/to/source but this one's easier to forget if your source and io.js version get out of sync! Mostly it doesn't matter if they aren't perfectly in sync if you have the right branch (just next and v1.x currently) checked out so the ABI matches.

[piscisaureus]

we really need to get the longer-term solution to node-gyp in there

Shipping the headers with the installer is something we should do also.
And indeed, I think we (as in io.js) should take control of node-gyp, and provide an end-to-end solution that doesn't only provide a build infrastructure but also the API (nan?) and possibly even the compiler itself.

[rvagg]

@TooTallNate would you be interested in "donating" node-gyp to the iojs org like I've done with NAN? it would mean more eyes and hands on the code to improve it over time, including the long desired ability to use locally installed headers rather than download if they are available.

[Fishrock123]

Closing in favor of #493

[jbergstroem]

(closing for @Fishrock123, guessing he hit the wrong button)