added instructions to install easy_install

Assuming a blank install of Ubuntu Stable (currently 12.04) it does not install "easy_install" and you need http://python-distribute.org/distribute_setup.py to do so.
clarified comment on distribute install for easy_install.
fixed typos and added a few more lines of detail

Fixed typos near the top mostly regarding needing sudo to change some things and to set up postgres. Great instructions. Yet as always they can still improve as I did find myself going off the path a few times and not documenting it.
Update nav caching to set a key instead of adding it.
Excluding status from PhotoBatchEditForm
Version bump to 5.1.194
New filter for File model: file_exists

- Checks if file exists at a disk level
Version bump to 5.1.195
#619: Custom forms field length validation for fields by type
Merge branch 'master' into bixly-testing