Don't re-download tarballs every time

Exact warning follows, WARNING:timestamping does nothing in combonation with -O

And, '-N' option to timestamp check. Just in case there really is a new
file.

Update crew

Modify the download method to specify an output filename

Update install.sh

Make sure wget outputs to the required filename

added tig - ncurses based Git browser

Dart SDK 1.5.3 binary package

Node.js 0.10.29

added ctags

Python 2.7.8 + commit order fix

Merge updates & fixes from @appelgriebsch