Make faulthandler handle multiple running ChimeraX instances

[Tom Goddard]

On Windows or Linux a user can easily start more than one instance of ChimeraX. When this happens the crash reporting sets up the Python faulthandler module to write to the same file for all instances. This can cause interleaved errors from different ChimeraX instances which are hard to make sense of. I am not sure if this ever happens. But ticket #6435 is an example where 3 fatal "access violation" errors are reported in the faulthandler output and it is hard to fathom how the first "access violation" did not kill the process.