The "running" attribute (readable through
gimp_backtrace_is_thread_running(), and recorded in the performance
log) specifies if the thread was in a running or suspended state at
the time the backtrace was taken.  It is accurate on Linux, but
only approximated on Windows.

Adapt the performance-log-expand.py tool to maintain this attribute
(and any future thread attributes we might add).

(cherry picked from commit 78adb7c9)