Usage: merge-rrd.py <old rrd> <new rrd> <merged rrd>
    
    merge-rrd.py is a python script that merges that data found in rrd
    files.  This assumes that the two rrds are have the same data structure.
    
    The script creates the merged rrd by copying the entries from the new rrd.
    If the new rrd has database entries with missing data, then the records
    of the old rrd are used instead.  This mean that data from the new rrd
    will always take precedence over the data in the old rrd.
    
    Please report any bug at:
     minhong.tsai@gmail.com                                    4-11-2005