made mktemp a requirement for building backupninja, added autotools variables to substitute the proper binary location and removed bad fall-back when mktemp was not there

sys: support selection of VServers to run on with the new vsnames configuration option (Closes: Trac#45)

lib/vserver: added vservers_running function, use it in sys handler (to ease future fix for Trac#45)

dup: support every duplicity-supported transport with new configuration option desturl (Closes: #483712, #346040, Trac#2)

 - general cleanup of dup handler
 - support remove-older-than command
 - also run "duplicity cleanup" before anything else, for safety reasons
 - migrated full/incremental backup switch to new syntax
ChangeLog: removed trailing space