Issue #2377: Make importlib the implementation of __import__().

importlib._bootstrap is now frozen into Python/importlib.h and stored
as _frozen_importlib in sys.modules. Py_Initialize() loads the frozen
code along with sys and imp and then uses _frozen_importlib._install()
to set builtins.__import__() w/ _frozen_importlib.__import__().
diff --git a/Python/frozen.c b/Python/frozen.c
index ddf6224..25fdc17 100644
--- a/Python/frozen.c
+++ b/Python/frozen.c
@@ -2,6 +2,7 @@
 /* Dummy frozen modules initializer */
 
 #include "Python.h"
+#include "importlib.h"
 
 /* In order to test the support for frozen modules, by default we
    define a single frozen module, __hello__.  Loading it will print
@@ -28,6 +29,8 @@
 #define SIZE (int)sizeof(M___hello__)
 
 static struct _frozen _PyImport_FrozenModules[] = {
+    /* importlib */
+    {"_frozen_importlib", _Py_M__importlib, (int)sizeof(_Py_M__importlib)},
     /* Test module */
     {"__hello__", M___hello__, SIZE},
     /* Test package (negative size indicates package-ness) */