Added ability to build node.js to ./do script

Added the function buildNode() to ./do, which downloads the source tar.gz, decompresses it, and builds it into the location where hasOkNode looks for it (./${BUILDDIR}/nodejs/node/bin/node is still the path of the binary). The script then goes on as before to build cjdns with node.js.

Building node.js still takes a pretty long time, even with the -j (jobs) flag optimally set on make.

As an added bonus, this pull request also updates the URLs on the ./do script to platform binaries (was 0.10.24, now updated to 0.10.25).