Update botan and fix the build

pkgs/development/libraries/botan/unstable.upstream

@@ -1,9 +1,10 @@
 url http://botan.randombit.net/download.html
-version_link 'Botan-[0-9]+[.][0-9]+([.][0-9]+)?[.](tbz|tbz2|tar[.]bz2)$'
+version_link 'Botan-[0-9]+[.][0-9]+([.][0-9]+)?[.](tgz|tbz|tbz2|tar[.]bz2)$'
 ensure_version
+attribute_name botanUnstable
 do_overwrite(){
   ensure_hash
-  set_var_value hash $CURRENT_HASH
+  set_var_value sha256 $CURRENT_HASH
   set_var_value baseVersion ${CURRENT_VERSION%.*}
   set_var_value revision ${CURRENT_VERSION##*.}
 }