Fix Issue10020 - Doc update to sqlite3 module in 2.7 branch.

Doc/library/sqlite3.rst

@@ -378,6 +378,8 @@ Connection Objects
 
    .. literalinclude:: ../includes/sqlite3/load_extension.py
 
+   Loadable extensions are disabled by default. See [#f1]_
+
 .. method:: Connection.load_extension(path)
 
    .. versionadded:: 2.7
@@ -386,6 +388,8 @@ Connection Objects
    enable extension loading with :meth:`enable_load_extension` before you can
    use this routine.
 
+   Loadable extensions are disabled by default. See [#f1]_
+
 .. attribute:: Connection.row_factory
 
    You can change this attribute to a callable that accepts the cursor and the
@@ -893,3 +897,11 @@ threads. If you still try to do so, you will get an exception at runtime.
 
 The only exception is calling the :meth:`~Connection.interrupt` method, which
 only makes sense to call from a different thread.
+
+.. rubric:: Footnotes
+
+.. [#f1] The sqlite3 module is not built with loadable extension support by
+  default, because some platforms (notably Mac OS X) have SQLite libraries which
+  are compiled without this feature. To get loadable extension support, you must
+  modify setup.py and remove the line that sets SQLITE_OMIT_LOAD_EXTENSION.
+