Fixes this ./configure symptom:
configure: WARNING: talloc.h not found, consider installing libtalloc-devel. Disabling cifs.upcall.
and is needed to (eventually) fix CIFS + DFS kernel mount on NixOS.
The updated version 5.9 couldn't mount any of my shares:
Status code returned 0xc000006d NT_STATUS_LOGON_FAILURE
CIFS VFS: Send error in SessSetup = -13
CIFS VFS: cifs_mount failed w/return code = -13
Apparently, this is a known problem in Windows Vista that needs to be
fixed on the server side. :-(
It turns out that mount.cifs is run in a shell environment that doesn't have
$PATH. To find that program, we must commit to some location. The path I used will
work fine on NixOS, but of course it won't work on other Linux distributions. I'm
not sure whether that's an important issue or not.
