SNMP fixes for OSX and added OID for enumerating Solaris Users

applied todb's snmp fixs for OSX https://dev.metasploit.com/redmine/issues/7480

added psProcessUsername MIB to snmp_enumusers - to additionally enumerate users on Solaris Systems
Reviewer: note that this diff is actually wrong ^ there are no changes to this file (you can double check against the copy on master).