Use pg_virtualenv for test.sh

Ref: https://github.com/yourlabs/django-autocomplete-light/pull/215#issuecomment-30764977
tests: use Django 1.6.1
tests: use `-r requirements.txt` for base requirements
tests: fix DJANGO_VERSION map for 1.6
Also import all exceptions in autocomplete_light/__init__.py
Use fixture prepared by setUp
Tested default autocomplete selection implementation
Added autocomplete_name attribute docstring
Added autocomplete_names support for modelform_factory
Documented autocomplete_names and default autocomplete logic
Import TaggitField and TaggitWidget in autocomplete_light/__init__.py
PEP8 removed blank line
Version bump 2.0.0a10
IE11 compability check
Indentation fix and added myself to AUTHORS for legal purposes
Version bump 2.0.0a11
Merge pull request #224 from blueyed/tests-pg_virtualenv

Fixes for test.sh: use pg_virtualenv
Warn that you are on v2
Make pg_virtualenv optionnal
Fix #236: Potential issue when django-taggit is not installed.