Hide pg deprecated constants warning

This is a temporary workaround to suppress the warning message
introduced when upgrading pg to 0.21.0 with an older version of
activerecord.

lib/pg/deprecated_constants.rb

@@ -0,0 +1,36 @@
+# Slightly modified version of a workaround written by Eliot Sykes https://stackoverflow.com/a/51232774
+# File: lib/pg/deprecated_constants.rb
+#
+# This file overrides the pg gem's pg/deprecated_constants.rb file and so
+# its warning message is not printed. Avoiding this warning message helps
+# clean up the app startup and test output.
+#
+# This behaviour relies on lib/ being ahead of the pg gem in $LOAD_PATH and
+# these lines from the pg gem's lib/pg.rb file:
+# autoload :PGError,  'pg/deprecated_constants'
+# autoload :PGconn,   'pg/deprecated_constants'
+# autoload :PGresult, 'pg/deprecated_constants'
+#
+# Your config/application.rb may need to modify autoload_paths to ensure
+# the lib/ dir is ahead of the pg gem install path in $LOAD_PATH:
+#
+# config.autoload_paths << Rails.root.join('lib')
+#
+if PG::VERSION != '0.21.0' || ActiveRecord.version.to_s != '4.2.11'
+  puts <<MSG
+-----------------------------------------------------------------------------------
+The pg and/or activerecord gem version has changed, meaning deprecated pg constants
+may no longer be in use, so try deleting this file to see if the
+'The PGconn, PGresult, and PGError constants are deprecated...' message has gone:
+#{__FILE__}
+-----------------------------------------------------------------------------------
+
+MSG
+end
+
+# Declare the deprecated constants as is done in the original 
+# pg/deprecated_constants.rb so they can still be used by older
+# versions of gems such as activerecord.
+PGconn   = PG::Connection
+PGresult = PG::Result
+PGError  = PG::Error