ckanext-spatial installation on Ubuntu 14 errors and notes:

Hi, going through a fresh installation of this extension I ran into the following notes and then some errors that prevented the postgis package_extent table from being created:

OS - Ubuntu Trusty 64b

The following commands (and sudo) are needed:
```
sudo pip install requests[security]
sudo pip install -e "git+https://github.com/ckan/ckanext-spatial.git#egg=ckanext-spatial" (this puts the clone src into local dir and not system path as advertised in docs even when activated in python virtualenv as outlined)
sudo apt-get install zlib1g-dev (required to build below cmd)
sudo pip install -r ./src/ckanext-spatial/pip-requirements.txt
```

Last it seems there are distribution errors on trusty:
```
(default) vagrant@vagrant-ubuntu-trusty-64:~/src$ sudo /usr/lib/ckan/default/bin/paster --plugin=ckanext-spatial spatial initdb 4326 --config=/etc/ckan/default/production.ini
Traceback (most recent call last):
File "/usr/lib/ckan/default/bin/paster", line 11, in
sys.exit(run())
File "/usr/lib/ckan/default/local/lib/python2.7/site-packages/paste/script/command.py", line 91, in run
commands = get_commands()
File "/usr/lib/ckan/default/local/lib/python2.7/site-packages/paste/script/command.py", line 133, in get_commands
plugins = pluginlib.resolve_plugins(plugins)
File "/usr/lib/ckan/default/local/lib/python2.7/site-packages/paste/script/pluginlib.py", line 83, in resolve_plugins
pkg_resources.require(plugin)
File "/usr/lib/ckan/default/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 891, in require
needed = self.resolve(parse_requirements(requirements))
File "/usr/lib/ckan/default/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 777, in resolve
raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound
```

These errors are using native python 2.7.6 with ubuntu trusty-64. Pip was installed via python-pip from apt repos.

Any suggestions are appreciated - thanks!

Start with the installation documentation and src/ckanext-spatial/pip-requirements.txt, then reproduce the listed Ubuntu Trusty setup commands. Use the paster spatial initdb command as the entry point and verify that installation completes without DistributionNotFound and the package_extent table is created.

Written by the indexing model from the issue text.