Quote value of MAN_DATE.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>

configure.ac

@@ -497,7 +497,7 @@ AC_SUBST(LIBS)
 dnl Libraries used only when building the mc binary
 AC_SUBST(MCLIBS)
 
-MAN_DATE=$(LC_ALL=C date "+%B %Y")
+MAN_DATE="$(LC_ALL=C date "+%B %Y")"
 AC_SUBST(MAN_DATE)
 
 AM_CONDITIONAL(USE_MAINTAINER_MODE, [test x"$USE_MAINTAINER_MODE" = xyes])