+20060421
+ + move most static variables into structures _nc_globals and
+ _nc_prescreen, to simplify storage.
+ + add/use configure script macro CF_SIG_ATOMIC_T, use the corresponding
+ type for data manipulated by signal handlers (prompted by comments
+ in mailing.openbsd.bugs newsgroup).
+ + modify CF_WITH_LIBTOOL to allow one to pass options such as -static
+ to the libtool create- and link-operations.
+