Applied patch from Dan Egnor improving the base64 code.

* base64.h (BASE64_ENCODE_LENGTH): New macro.
(struct base64_ctx): New context struct, for decoding.
(BASE64_DECODE_LENGTH): New macro.
* base64.c (base64_decode_init): New function.
(base64_decode_update): New function, replacing base64_decode.
Takes a struct base64_ctx argument.
* configure.in: Use AC_PREREQ(2.50).

Rev: src/nettle/configure.in:1.10

configure.in

@@ -5,6 +5,8 @@ dnl Process this file with autoconf to produce a configure script.
 
 AC_INIT(arcfour.c)
 
+AC_PREREQ(2.50)
+
 AM_INIT_AUTOMAKE(nettle, 1.5)
 
 AM_CONFIG_HEADER(config.h)