Make PGLO-READ a generic function, with specializations on the v2 and
v3 protocols. The difference is necessary because the v2 protocol
reads large-object data in text, whereas the v3 protocol changed to
use a binary format.

darcs-hash:6639fd1b9dd10ca051ea03d7e2fbff94c0d917e2

- improvements to the system-dependent functionality: OpenMCL is
    able to use a local connection to the backend; most
    implementations resignal connection errors as a postgres-error.

  - fixes to the lowlevel code

darcs-hash:81350b160619ff22468166aa3f1928c8f75d9b7e

- fix to the lowlevel factorization

 - modify parameter handling in v3 protocol to add parameters to the
   connection object, instead of issuing a warning

darcs-hash:82327edc147c2403516468713a8c403b5b6d0648

More factorization of lowlevel functions between v2 and v3 protocols.

darcs-hash:aef9e7feac79e0d6b749d3ff999a62e1f50c4d69