Optimizations for bytes reallocation. This uses up to 12.5% overallocation, not entirely unlike list_resize(). Could probably use more tweaks for odd allocation patterns, TBD. Also add __alloc__() method which returns the actually allocated size. PS. I'm now convinced that we need something like "".join(); later.

--- a/Include/bytesobject.h	Sun Apr 30 02:32:45 2006 +0000
+++ b/Include/bytesobject.h	Fri May 05 04:34:18 2006 +0000
@@ -21,6 +21,7 @@
 /* Object layout */
 typedef struct {
     PyObject_VAR_HEAD
+    Py_ssize_t ob_alloc; /* How many bytes allocated */
     char *ob_bytes;
 } PyBytesObject;