Some improvements on the devel build

This is partially addressing #1149 and some discussion happening in #1518

Essentially it simplify the build script a little bit and add some new behaviour/functionality:
* The script create a local tag in the current HEAD and take that to build the name of the package: Now you pass the string `0.7.1-devel` to the script, and that would be the tag and, for instance, this would be the name: `bokeh-0.7.1.devel.f5b9b75-np19py34_1.tar`, where 0.7.1 it is the same than before, but now, we are not using the date anymore, instead the commit sha from that revision point. That's prevent errors when you upload two or more devel builds at the same time (and will also be useful to determine the exact point where a bug comes appear).
* You can pass the Rackspace user and key API (you can use env var too) and it will push devel build form of the bokeh.[min].js and bokeh.[min].css files but with the version included, for instance: `bokeh.0.7.1.devel.f5b9b75.js`
* The script also take care of deleting all the build stuff we generated, including the malicious `__conda_verision__.py`. It also delete the converted packages, `dest/` and `build/`.

I can imagine a lot of enhancement... and some of then were discussed in #1149. But, this is functional as is and I plan to use it tomorrow to upload a devel build, as a functionality test. We can probably merge this soon, after the review, and then iterate on other changes in a new PR.

Damian