possible resource leak, connection not always actively destroyed

[Robert]

We create libpq connections with initPQConn:

pg-client-hs/src/Database/PG/Query/Connection.hs

Line 154 in 5e8a2d7

 conn <- PQ.connectdb (pgConnString $ ciDetails ci) 

1. Then if we're not happy with the connection (or something goes wrong figuring that out), we throw it away, leaving the call to PQfinish to the foreign pointer finalizer.

2. In the pool initializer:

   pg-client-hs/src/Database/PG/Query/Pool.hs

   Line 115 in 5e8a2d7

    pqConn  <- initPQConn ci logger 

   , the connection created by initPQConn will again not be finalized if something goes wrong later in the creator (e.g. exception thrown by EKG.Distribution.Add).