Fix memory leak in dev mode for jobs / msg procs (TORQUE-1029)

Scheduled jobs and message processors were leaking memory at a
substantial rate in development mode when Rails 3.2+ was in use. This
possibly impacts earlier Rails versions as well but has only been
confirmed to be an issue on Rails 3.2.
Don't accidentally change marshalled string encodings (TORQUE-1073)

When concatenating a literal string with the value produced by
Marshal.dump, it can end up changing the marshalled string encoding
from ASCII-8BIT to UTF-8 or something else, depending on the default
locale. Change our MARSHAL_MARKER to a marshalled string value so that
we aren't changing encodings with concatenation.