Add python-pycurl to list of base packages
Add early APT cache update to avoid stale cache

This should fix problems with missing packages in Travis builds - they
are not "missing", but new version has been uploaded to repository, and
system images have not updated their default package lists yet.
Merge pull request #27 from drybjed/apt/base_packages

Add python-pycurl to list of base packages
Add support for PostgreSQL PGDG APT repository

PostgreSQL Global Development Group APT repository maintains packages
for different PostgreSQL versions as well as additional software. More
information: https://wiki.postgresql.org/wiki/Apt

PGDG APT repository can be enabled by setting 'postgresql_pgdg' boolean
variable to True.
Add support for PostgreSQL 9.3 in 'postgresql'

To install PostgreSQL 9.3, you need to enable PGDG APT repository and
change 'postgresql_version' variable to "9.3".
Merge pull request #28 from drybjed/role/postgresql

Updates in 'postgresql' role