add OSX 10.9 version flags

TODO: here, Xcode 6.0.1 and OS10.9.5  mmacosx-version-min=10.5 works
and produces binaries compatible with 10.5 or later, but that may 
no be standard. - Please x-check, for now 10.8 should work everywhere.

wscript

@@ -301,6 +301,11 @@ def set_compiler_flags (conf,opt):
         compiler_flags.extend(
                 ("-DMAC_OS_X_VERSION_MIN_REQUIRED=1070",
                  '-mmacosx-version-min=10.7'))
+
+    elif conf.env['build_target'] in [ 'mavericks' ]:
+        compiler_flags.extend(
+                ("-DMAC_OS_X_VERSION_MAX_ALLOWED=1090",
+                 "-mmacosx-version-min=10.8"))
     else:
         conf.define ('IS_OSX', 0)