Because it doesn't make sense to replace the date placeholder at
process creation, it has to be replaced at every start of the process.
On process creation only the static placeholders (such as process ID)
are replaced. Dynamic placeholders (so far only "date") are not
replaced. On process start, a callback has been introduced that gives
the chance to change the command line. This is the point where
the restreamer replaces the date placeholders.
