Programs that want to background themselves now need
to define threadmaybackground returning 1.
This avoids a confusing (to people and debuggers)
extra parent process for all the threaded programs
that will never want to background themselves.

Remote whitespace at the ends of lines.
Remove blank lines from the ends of files.
Change modes on source files so that they
are not executable.

Signed-off-by: Dan Cross <cross@gajendra.net>

thanks to Erik Quanstrom

R=rsc
http://codereview.appspot.com/3469042

http://bitbucket.org/rsc/plan9port/issue/38/

This patch tries to make 9pserve work again with
9P2000 clients, in case the server handled by 9pserve
expects 9P2000.u.

(Since changeset
http://bitbucket.org/rsc/plan9port/changeset/d9843471f0bc/
servers using srv() stop communicating after they
received a 9P2000 msg that has a different .u
definition.)

Tattach, Tauth and Tcreate 9P2000 messages will
be translated now, if neccessary, to 9P2000.u by
growing them to the new size, and providing the
missing (default) values.

The code of the first two message types has been
tested with drawterm on linux (dialing factotum),
and mounts from within 9vx to plan9port's factotum
and dossrv.

The code for Tcreate couldn't be tested due to lack
of file servers both speaking 9P2000.u and allowing file
creation.

R=rsc_swtch, rsc
CC=codebot
http://codereview.appspot.com/151052

Just like outputthread can have processed the message
but not yet called msgput, the same is true of the
connoutthread, so we cannot check c->nmsg until
after the connoutthread has shut down gracefully.