[Halld-offline] Random number seeds in mcsmear

[David Lawrence]

Hi All,

   I have committed changes to the repository this morning to implement 
the storage and retrieval of the random number seeds used by mcsmear. 
This required several changes:

1.) The random number generator used in mcsmear was changed from 
TRandom3 to TRandom2. This is because the former uses 624 random number 
seeds and the latter only 3. TRandom2 does have a period of 10^26 so 
this should still be sufficient.

2.) The HDDM data model was modified to include slots for the 3 seeds 
that need to be stored every event. This means old HDDM files will cause 
warnings when being read into executables linked with the new data 
model. They should still work except for the new random seed features 
may not function properly.

3.) An option "-i" was added to mcsmear to allow one to specify that any 
seeds found in the input HDDM file should be ignored. Thus, allowing one 
to re-run mcsmear using the same input file and get a different result. 
This was previously the default behavior with no option to change it. 
Note that if you are using a file with no mcsmear seeds in it (the most 
common case), specifying "-i" will have no effect and the sequence will 
be different each time you run mcsmear with that input file.

Please let me know if you run into any problems with hdgeant or mcsmear 
related to these changes or if you have any questions.

Regards,
-David