Backport the ODBC Loader to work against the Vertica 6.0 SDK (with an ex...

Backport the ODBC Loader to work against the Vertica 6.0 SDK (with an extra option to 'make').  6.0 users lose some rarely-used 6.1-specific features with this option; most people should be unaffected.

Update the README accordingly.  Also, take this opportunity to update the README generally.