Rewrote decode_public_key to use Stdio.Buffer
Support for decoding secret keys.
Protocols.LDAP: Corrected doc for client().
Image.ANY: fix use after free
Image.GIF: sanity check maxcode
Image.PNG: do length check before checking for IEND
Image.GIF: Fix leak

Cloning of Image objects can throw exceptions. Push the colortable to
the stack early, to prevent it from leaking in case of an error.
SSL.File: Improved API for resuming sessions somewhat.