Print tracebacks for unraisable exceptions by default.

These are usually errors, and this is useful debug information to have.
It can still be disabled via a directive.

CHANGES.rst

@@ -14,7 +14,7 @@ Features added
 
 * Support pyximport from zip files.
   Patch by Sergei Lebedev (Github issue #1485).
-  
+
 * IPython magic now respects `__all__` variable.  Also skips
   leading-underscore values (like `import *`).
   Patch by Syrtis Major (Github issue #1625).
@@ -45,6 +45,11 @@ Bugs fixed
 * File paths of code objects are now relative.
   Original patch by Jelmer Vernooij (Github issue #1565).
 
+Other changes
+-------------
+
+* The `unraisable_tracebacks` now defaults to `True`.
+
 
 0.25.2 (2016-12-08)
 ===================

Cython/Compiler/Options.py

@@ -173,7 +173,7 @@ _directive_defaults = {
     'c_string_type': 'bytes',
     'c_string_encoding': '',
     'type_version_tag': True,   # enables Py_TPFLAGS_HAVE_VERSION_TAG on extension types
-    'unraisable_tracebacks': False,
+    'unraisable_tracebacks': True,
     'old_style_globals': False,
 
     # set __file__ and/or __path__ to known source/target path at import time (instead of not having them available)