BIG patch...

BIG patch...

This patch makes Samba compile cleanly with -Wwrite-strings.
 - That is, all string literals are marked as 'const'.  These strings are
always read only, this just marks them as such for passing to other functions.

What is most supprising is that I didn't need to change more than a few lines of code (all
in 'net', which got a small cleanup of net.h and extern variables).  The rest
is just adding a lot of 'const'.

As far as I can tell, I have not added any new warnings - apart from making all
of tdbutil.c's function const (so they warn for adding that const string to
struct).

Andrew Bartlett