How to determine installed package version

[Boris Kovalenko]

Hello!

    I'm sorry if I'm writing wrong list. I'm a Quagga port maintainer 
and want to simplify user selection of SNMP lib via DIALOG. As I found, 
there are only to ports of SNMP lib for FreeBSD - NetSNMP v5 and old 
UCD-SNMP v4. I want to check what version of SNMP lib user have 
installed and precheck apropriate option. Is there a RIGHT way to do that?

Yours truly,
    Boris Kovalenko