Fixed problem with tra script, and changed get_traces

get_traces.cpp:
No longer calls gnuplot by default, that is now done by the
-g, --gnuplot switches. This was causing problems when one used the
scripts from within gnuplot itself.

tra:
This has been updated to use the proper program/scripts to get/plot the
traces.

Signed-off-by: S.V. Paulauskas <stanpaulauskas@gmail.com>