* adds support for `--psol-from-source` so you don't need binary modules, and `--devel` so you can run our tests without going and getting all our dependencies
* adds submodules for testing: mod_pagespeed, ngx_cache_purge etc
* adds support for running as:
```
git clone git@github.com:pagespeed/ngx_pagespeed.git
cd ngx_pagespeed/
git checkout <branch>
scripts/build_ngx_pagespeed.sh [options]
```
* depends on the scripts @hillsp is working on so that we can just check out mod_pagespeed and ask it to build and rebuild itself
* adds colors to output to make it easier to read
* always run with a clean cache
* in the future we should structure the tests so they run twice, once with a clean cache and then again with a populated one, but for now a clean cache should catch more bugs
* stop requiring a file cache path for tests; just use
* fix exit codes to match documentation at the top of the file: 1 is a test failure, 2 is bad args
Squash-merge of my #198.
We are going to need some nginx-specific system tests, and this seemed like a
good place to start. This adds two tests, as well as some infrastructure. With
Squash-merge of my #194 and #195
Jeff Kaufman