NRPE_NT Code

r45 did huge changes with an empty log message. These two commits also
broke a lot of things. Some of these have been again fixed in later
revisions, but not all. In detail, this reverts does:

* Changes back the timestamp logging code. The CHANGELOG says "fixed
timestamp in nrpe_nt.log", but I don't see what wrong with the
earlier code.

* Removed the loglevel config param. Hard to exclude from the
revert. If only this feature had been atomically committed from the
beginning...

* Reverts the file version, to avoid any confusion. We will bump up to
a new major in a near future.

* Reverted the handling of argument characters (ALLOWED_ARGUMENT_CHARS
vs NASTY_METACHARS and NASTY_METACHARS_WIN). Again, the commit
contained no motivation whatsoever why this change was done.

* Again supporting prefetch commands.

* Removed the delay_shutdown feature. Again, hard to exclude, and
there's no real motivation for it.