Bug#88340: Use "chown user:group", not "chown user.group"

[Marek Michalkiewicz <marekm@amelek.gda.pl>]

> I fail to see how this affects Debian?  We use the GNU tools.  The chowns
> happening in maintainer scripts and elsewhere are for a known set of names
> and so will not be affected by this. 

Well, the GNU tools manual recommends using ':', and I think standards
compliance is a good thing too (and it is very easy in this case).

OK, perhaps my proposal to make GNU chown fail on '.' was a bit extreme,
but printing a warning wouldn't be a bad idea IMHO.

Changing "chown user.group" to "chown user:group" is not something very
urgent (no need for a new upload just for this change), but I think it
would also be good to document this in the policy manual (the section
about scripts).

(Speaking of scripts: some people say they should start with the "#! /"
magic, not "#!/" - but I'm not sure where this came from...  Anyone?)

Thanks,
Marek