Enable the checks to actually work with xulrunner-1.9.1.x series which upstream
never enabled.

--- configure.ac~	2009-08-20 23:37:39.052828677 -0500
+++ configure.ac	2009-08-20 23:39:01.608828817 -0500
@@ -5534,6 +5534,7 @@
     AS_IF( [test $found = 1],[
         CPPFLAGS="${CPPFLAGS_save} ${MOZILLA_CFLAGS}"
         MOZILLA_REQUIRED_HEADERS=1
+        AC_CHECK_HEADERS([npfunctions.h])
         AC_CHECK_HEADERS(npapi.h,,MOZILLA_REQUIRED_HEADERS=0)
         AC_CHECK_HEADERS(npruntime.h,,MOZILLA_REQUIRED_HEADERS=0,
           [#if HAVE_NPAPI_H

--- config.h.in~	2009-08-20 23:37:47.795805490 -0500
+++ config.h.in	2009-08-20 23:39:37.015805699 -0500
@@ -541,6 +541,9 @@
 /* Define to 1 if you have the <npapi.h> header file. */
 #undef HAVE_NPAPI_H
 
+/* Define to 1 if you have the <npfunctions.h> header file. */
+#undef HAVE_NPFUNCTIONS_H
+
 /* Define to 1 if you have the <npruntime.h> header file. */
 #undef HAVE_NPRUNTIME_H