improve comments and messages as suggested

diff --git a/Zend/acinclude.m4 b/Zend/acinclude.m4
index cec832fccb9fe4847c0c663aaedbdaee4109d65f..db6aee2f4af3b79906894d201b4694b7e7829e88 100644 (file)
--- a/Zend/acinclude.m4
+++ b/Zend/acinclude.m4
@@ -3,10 +3,13 @@ dnl
 dnl This file contains local autoconf functions.
 
 AC_DEFUN([LIBZEND_BISON_CHECK],[
-  # we only support certain bison versions, min: 2.4
+  # we only support certain bison versions;
+  # min: 2.4 (i.e. 204, major * 100 + minor for easier comparison)
   bison_version_min="204"
-  # non-working versions, e.g. "3.0 3.2"
-  bison_version_exclude=""
+  # non-working versions, e.g. "3.0 3.2";
+  # remove "none" when introducing the first incompatible bison version an 
+  # separate any following additions by spaces
+  bison_version_exclude="none"
 
   # for standalone build of Zend Engine
   test -z "$SED" && SED=sed