Initial version of support for Colasoft Capsa files.

The time stamp origin is not correct.  Capsa's absolute time stamp for
the sample captures from their Web site would be helpful.

Change-Id: I365daf7b42240e33f54df76939254f41ed57a9b2
Reviewed-on: https://code.wireshark.org/review/4671
Reviewed-by: Guy Harris <guy@alum.mit.edu>