build: make python development headers not mandatory in standalone libs

This needed an update to the python tool in waf

thanks to Kai for spotting this

lib/tdb/wscript

@@ -46,7 +46,7 @@ def configure(conf):
         # also disable if we don't have the python libs installed
         conf.check_tool('python')
         conf.check_python_version((2,4,2))
-        conf.check_python_headers()
+        conf.check_python_headers(mandatory=False)
         if not conf.env.HAVE_PYTHON_H:
             Logs.warn('Disabling pytdb as python devel libs not found')
             conf.env.disable_python = True