Really bail out if a check for a required package fails.

m4/check-package.m4

@@ -455,7 +455,9 @@ m4_if(alb_ac_HEADERS,[],[],[
 if test -n "$[]UPNAME[_LIBS]"; then
   AC_MSG_RESULT([**** Successfully finished checks for OPTIONAL package alb_ac_PKGNAME ****])
 else
-  AC_MSG_RESULT([**** Checks for OPTIONAL package alb_ac_PKGNAME finished UNSUCCESSFULLY ****])
+  m4_if(OPTIONAL,[required],
+    [AC_MSG_ERROR([**** Checks for required package alb_ac_PKGNAME finished UNSUCCESSFULLY ****])],
+    [AC_MSG_RESULT([**** Checks for optional package alb_ac_PKGNAME finished UNSUCCESSFULLY ****])])
 fi])
 
 fi dnl disable fi