illumos gate

This may be desired behaviour, I am not sure, but seems to me that having any undocumented flags is bad juju. The `-m` flag, used only really by the system log service on startup to save any messages from dumps on the system is seemingly not mentioned in either usage() or the man page.

Someone looking at the startup for system log may be wondering what it does, or generally wonder how messages from savecore make it into the system log. At any rate, seems like this should be changed, and really should be a matter of adding `m` to usage() message and bumping the man page.

This could be a good updated manpage to use: https://gist.github.com/szaydel/e8f156149cc1fe9d7843/#file-savecore-1m