Remove "unsupported version" warning for Greenplum

Hello,

we tested pgAdminIII 1.22 internally and found that it works sufficient
with Greenplum. A few minor problems are identified and we plan to work
on them as well, but nothing serious. We however know that there are a
number more serious problems with HAWQ (SQL on Hadoop), we plan to work
on this as well.

As a first step, attached is a patch which removes the "unsupported
version" warning for Greenplum. The patch copies a bit infrastructure
and prepares us to support later versions of Greenplum when we bump our
version number after merging with later PostgreSQL versions. One
remaining question is if the supported versions should stay in
pgConn.cpp or move to pgAdmin3.h.

Thank you,

--
Andreas 'ads' Scherbaum
German PostgreSQL User Group
European PostgreSQL User Group - Board of Directors
Volunteer Regional Contact, Germany - PostgreSQL Project