contrib/mtn2git/mtn2git.py: Built a fifo to avoid parsing the manifests all over...

contrib/mtn2git/mtn2git.py: Built a fifo to avoid parsing the manifests all over again
    I decided to use a FIFO for two reasons:
        -Simplicity in the implementation
        -Parent and Childs are normally close (<= 100 revisions) to each other. So having
         the fifo should avoid parsing the parent manifest over and over again. Also with
         "merge early and merge often" the 100 revs should be enough to catch merges as well.