added command line switch '-z' which lets one specify a Z39.50 proxy through which...

added command line switch '-z' which lets one specify a Z39.50 proxy through which the Z39.50 requests are tunneled.
This is planned to be used to stack a MetaProxy after a Paraz2 to make authentification stuff and database filtering stuff (special record conversions needed, or PQF-to-PQF manipulation) at the MetaProxy level. The '-z' option sends Z39.50 packages to the host:port specified there, with the origial target host:port addd in a vHost soecialinfo structure