Add an informative __main__.py (#620)

* Add an informative __main__.py

Give users an easy way to figure out what versions they're running.

* Why not more info!

* Add test

* No empty last line

* Make @alex happy

* DIAF Python 2.6

* Add cffi's version

* Make debug a module

* Add cryptography's compile-time OpenSSL
diff --git a/tests/test_debug.py b/tests/test_debug.py
new file mode 100644
index 0000000..2d62a3a
--- /dev/null
+++ b/tests/test_debug.py
@@ -0,0 +1,10 @@
+from OpenSSL.debug import _env_info
+from OpenSSL import version
+
+
+def test_debug_info():
+    """
+    Debug info contains correct data.
+    """
+    # Just check a sample we control.
+    assert version.__version__ in _env_info