MEDIUM: startup: call chroot() if needed in one place

MEDIUM: startup: call chroot() if needed in one place

There are two 'chroot' code blocks, both under quite same:

	'if ((global.mode & (MODE_MWORKER|MODE_DAEMON...)...'

The first block serves to perform chroot only for process in the foreground
mode. The second comes after master-worker fork and allows to do chroot
in daemon and in worker modes.

Due to moving the master-worker fork in init() in some previous commit, the
second 'chroot' code block now is no longer under the 'if'. So, it is executed
for all modes, except MODE_MWORKER. Now in MODE_MWORKER process enters in its
wait polling loop just after forking a worker and it terminates almost
immediately, if it exits this loop.

Worker, daemon and process in a foreground mode will perform the chroot as
before, but now it will be done in a one place at main().