[master] fixed a build failure on freebsd8/g++: we need to include Python.h

before everything else as requested in
http://docs.python.org/py3k/extending/extending.html#a-simple-example

src/lib/dns/python/tsigerror_python.cc

@@ -12,6 +12,8 @@
 // OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 // PERFORMANCE OF THIS SOFTWARE.
 
+#include <Python.h>
+
 #include <string>
 #include <stdexcept>