[Exim] updated uvscan local_scan()

Hi,

I'm preparing an updated version of L001, hopefully in time to make the
Exim 4.20 documentation. The new version will show off a little more of
the API (eg configuration file options, ability to freeze messages).

http://www.dcs.qmul.ac.uk/~mb/local_scan/local_scan.c

Enjoy. Please let me know if it behaves unexpectedly.

Matt