Bump AC_PREREQ to 2.53.
diff --git a/configure b/configure
index 230056b..48467c9 100755
--- a/configure
+++ b/configure
@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Revision: 1.305 .
+# From configure.in Revision: 1.306 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.53.
 #