Add support for sorting caret ('^') higher than base version
    
    1.1^20160101 means 1.1 version (base) and patches which were applied at
    that date on top of it.
    
    * 1.1^201601 > 1.1
    * 1.1^201601 < 1.1.1
    
    Having symmetry is also good.
    
    Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>