Some changes to the handling of aborted calculations

Description

A couple of changes to the code behavior when a calculation aborts:

• the walltimer now uses the messages_switch_status routine to create the status file.
• switch the status file to aborted when handling a signal.
• to make the previous change useful, trap signals by default.

News snippet

A couple of changes to the code behavior when a calculation aborts.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.