Drop Postgresql 9.0 and add 9.3 support

Signed-off-by: Sylvain Rabot <sylvain@abstraction.fr>
sql: Fix pg_size_pretty call

On Postgresql 9.1 pg_size_pretty(numeric) does not exist.

Signed-off-by: Sylvain Rabot <sylvain@abstraction.fr>
Makefile: double quote some vars

Signed-off-by: Sylvain Rabot <sylvain@abstraction.fr>
Makefile: move sections around in order to init vars correctly

Signed-off-by: Sylvain Rabot <sylvain@abstraction.fr>
Add continuous integration with Travis

Signed-off-by: Sylvain Rabot <sylvain@abstraction.fr>