MFH:- Prevent errors in CVS builds when bison is not there (for Sean :)

configure.in

@@ -165,6 +165,15 @@ PHP_PROG_AWK
 PHP_PROG_BISON
 PHP_PROG_RE2C
 
+dnl Check if bison generated files exist when bison does not..
+case $php_cv_bison_version in
+  ""|invalid[)]
+    if ! test -f "$abs_srcdir/Zend/zend_language_parser.h" || ! test -f "$abs_srcdir/Zend/zend_language_parser.c" ; then
+      AC_MSG_ERROR([bison is required to build PHP/Zend when building a CVS checkout!])
+    fi
+    ;;
+esac
+
 PHP_ARG_ENABLE(re2c-cgoto, whether to enable computed goto gcc extension with re2c,
 [  --enable-re2c-cgoto     Enable -g flag to re2c to use computed goto gcc extension], no, no)