redoconf: a stub rc_include() now sources ./redoconf.rc automatically.

This lets us remove the awkward ". ./redoconf.rc" line from zillions
of .od scripts, without paying the price of *always* including that
whole file every time default.do.sh is used.

redoconf/default.do.sh

@@ -14,6 +14,11 @@ die() {
     exit 99
 }
 
+rc_include() {
+	. ./redoconf.rc || exit 1  # redefines rc_include
+	rc_include "$@"
+}
+
 _mkdir_of() {
 	local dir="${1%/*}"
 	[ "$dir" = "$1" ] ||