strace-log-merge: work around corner cases of strace -ttt parsing

strace-log-merge: work around corner cases of strace -ttt parsing

Employing strace -ttt for the logs destined to be fed to
strace-log-merge is ultimately the best solution except for the logs
that pass the following dates:

Thu Jan  1 00:00:09 UTC 1970
Thu Jan  1 00:01:39 UTC 1970
Thu Jan  1 00:16:39 UTC 1970
Thu Jan  1 02:46:39 UTC 1970
Fri Jan  2 03:46:39 UTC 1970
Mon Jan 12 13:46:39 UTC 1970
Sun Apr 26 17:46:39 UTC 1970
Sat Mar  3 09:46:39 UTC 1973
Sun Sep  9 01:46:39 UTC 2001
Sat Nov 20 17:46:39 UTC 2286
Wed Nov 16 09:46:39 UTC 5138
Fri Sep 27 01:46:39 UTC 33658
Sun May 20 17:46:39 UTC 318857
Sat Nov  7 09:46:39 UTC 3170843
Sun Jul  5 01:46:39 UTC 31690708
Sat Jan 25 17:46:39 UTC 316889355

Let's lift this limitation.

* strace-log-merge: Generate numeric-only key for sorting, use sort -n
option.