Fix regression in "includes" argument in yara.compile. With includes=True…

Fix regression in "includes" argument in yara.compile. With includes=True includes were being disabled instead of enabled.

Closes #78.

tests.py

@@ -755,7 +755,7 @@ class TestYara(unittest.TestCase):
         r = yara.compile(p2)
         self.assertTrue(len(r.match(data='dummy')) == 2)
 
-        self.assertRaises(yara.SyntaxError, yara.compile, source='include "test"', includes=False)
+        self.assertRaises(yara.SyntaxError, yara.compile, source='include "test2"', includes=False)
 
     def testExternals(self):
 

yara-python.c

@@ -1894,7 +1894,7 @@ static PyObject* yara_compile(
       if (PyBool_Check(includes))
       {
         // PyObject_IsTrue can return -1 in case of error
-        if (PyObject_IsTrue(includes) == 1)
+        if (PyObject_IsTrue(includes) == 0)
           yr_compiler_set_include_callback(compiler, NULL, NULL, NULL);
       }
       else