++ Command line:
    /home/afniHQ/ -help

Helpfile for:    ***  ***
Version num:     1.21
Version dat:     Dec 5, 2018
Written by:      PA Taylor (NIMH, NIH)

Just a simple helper function for the fat_proc* scripts.

Takes >= 3 arguments:
   1) an output file name;
   2) an int that is the upper index for the selector (-1 means
      just use the max number in the input strings)
   3) 1 or more string selector strings of *goods* to keep

Converts those string selectors to a list of ints, then
intersectionizes all the lists, and then spits out a new string
selector (with ',' and '..'  notation) to the output file.