Fix Travis build

A few fixes:

- Removed UbuntuGIS-unstable since Travis now ships with PostGIS and PostgreSQL

- The latest version of pip is more strict and since ModestMaps is not hosted
  by Pypi, it needs the --allow-external ModestMaps --allow-unverified ModestMaps flags

- The recommended way to setup databases in Travis is to use the before_script
  section.
Fix import errors for case-insensitive filesystems

If you have a case-insensitive filesystem (or even a VM running on
top of a case-insensitive filesystem) you will get import errors.

For example, TileStache's Mapnik.py has an "import mapnik" call.
Since the filesystem is not distinguishing mapnik.py from Mapnik.py
it re-imports itself and then fails. We can fix this by enabling
absolute imports.
Remove 'host' from test conn strings
Add TileStache Vagrant Machine

Install Vagrant ( http://www.vagrantup.com/ ).

If you execute:
      vagrant up

You will get an Ubuntu 14.04 LTS with all the dependencies
installed.

To run the Tilestache tests:

cd /srv/tilestache
./runtests.sh
Fix travis memcache travis tests

The memcached-related tests were failing because they
could not connect to memcached. Travis has its own way
of starting certain services - memcached being one of
them.
Merge branch 'amigocloud_fixes' of https://github.com/rburhum/TileStache
Bumped to 1.49.10 with testing fixes from Amigocloud