Add a new `W' flag, that when used in conjunction with the `Z' flag or the

Add a new `W' flag, that when used in conjunction with the `Z' flag or the
`J' flag means that newsyslog should wait for previously started compression
jobs to complete before starting a new one for this entry.  When it is used
along with the `G' flag, in the case when several logfiles match the pattern
and should be compressed, the newsyslog will compress logs one by one,
ensuring that only one compression job is running at a time.

This prevents newsyslog(8) from overloading system by starting several
compression jobs on big files simultaneously.

Sponsored by:	Porta Software Ltd
MFC after:	2 weeks