passwordcheck: Log cracklib diagnostics

A user tried to use the cracklib build-time option of the passwordcheck 
module.  This failed, as it turned out because there was no dictionary 
installed in the right place, but the error was not properly reported, 
because the existing code just throws away the error message from 
cracklib.  Attached is a patch that changes this by logging any error 
message returned from the cracklib call.

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Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services