Avoids bailing on non-zero exit status from commands. This will lets

Avoids bailing on non-zero exit status from commands.  This will lets
us collect as many stats as possible, even when a test for a revision
in the middle of the list fails due to a bug.
Updates the "baseline" timing revision (the revision that has
the earliest "stable" TimeSCons infrastructure
Removes --noqmtest, since the "baseline" revision no longer uses
QMTest by default.
Changes the --logfiles option to a --logsdir option.
Updates the usage message.

git-svn-id: http://scons.tigris.org/svn/scons/trunk@4558 fdb21ef1-2011-0410-befe-b5e4ea1792b1