(maint) also catch Psych::SyntaxError

Psych::SyntaxError is a RuntimeException. This still needs to
catch that. This was uncovered by the recent move to catch StandardError
rather than the catchall Exception that was here before.

lib/puppet/parser/functions/parseyaml.rb

@@ -16,7 +16,10 @@ be returned if the parsing of YAML string have failed.
 
     begin
       YAML::load(arguments[0]) || arguments[1]
-    rescue StandardError => e
+      # in ruby 1.9.3 Psych::SyntaxError is a RuntimeException
+      # this still needs to catch that and work also on rubies that
+      # do not have Psych available.
+    rescue StandardError, Psych::SyntaxError => e
       if arguments[1]
         arguments[1]
       else