Blacklist PGI from using conformant array parameters. (#511)

* Blacklist PGI from using conformant array parameters.

There is a bug in pgcc with conformant array parameters where the
length argument is a pointer which triggers a compiler error
(PGC-S-0094, to be specific).  The issue has been reported to PGI and
is being tracked internally as TPR 23778.  For more information, see

  https://www.pgroup.com/userforum/viewtopic.php?t=5501

* travis: Add PGI Community Edition build.

For details on the installation script, see
https://github.com/nemequ/pgi-travis