Produce vala debug information
    
    Build with 'valac -g' to make sure we have good vala debug information.
    gnome-contacts has a history of crashing fairly often so it's important
    to get good backtraces to be able to work with upstream.
    
    Most (all?) of the debug info is just going to get split out into
    -debuginfo and -debugsource subpackages, so it shouldn't affect runtime
    much, if at all.