Updated runtime files. Remove version checks for Vim older than 6.0.

runtime/syntax/redif.vim

@@ -7,10 +7,8 @@
 " File Extension:    rdf
 " Note:              The ReDIF format is used by RePEc.
 
-" To be compatible with Vim 5.8 use:
-if version < 600
-  syntax clear
-elseif exists("b:current_syntax")
+" quit when a syntax file was already loaded
+if exists("b:current_syntax")
   finish
 endif