freebsd install execinfo's header to /usr/local, add it to include path.

wscript

@@ -128,7 +128,7 @@ def configure(conf):
   if Options.options.efence:
     conf.check(lib='efence', libpath=['/usr/lib', '/usr/local/lib'], uselib_store='EFENCE')
 
-  if not conf.check(lib="execinfo", libpath=['/usr/lib', '/usr/local/lib'], uselib_store="EXECINFO"):
+  if not conf.check(lib="execinfo", includes=['/usr/include', '/usr/local/include'], libpath=['/usr/lib', '/usr/local/lib'], uselib_store="EXECINFO"):
     # Note on Darwin/OS X: This will fail, but will still be used as the
     # execinfo stuff are part of the standard library.
     if sys.platform.startswith("freebsd"):