Ditz issue update
Add duk_{get,set}_prototype() to API

Right now duk_set_prototype() allows prototype loops which is OK as such but
prototype loops haven't previously been allowed.  There's at least one issue
in mark-and-sweep which causes an uncaught error when a prototype loop is
present.
Add flushes to runtests.js C stdout
Debug log uncaught error
FIXME notes and other trivia
Add 'ignore prototype loop' flag to desc lookup

This is not ideal for the generated asm code but optimization can be done
separately.
Add an API testcase for prototype loop and GC
Draft API testcase for duk_{get,set}_prototype
Prototype loop fix for error augmentation

Add an ignore_loop argument to duk_hobject_prototype_chain_contains() to
support this behavior.  It depends on the context whether a prototype loop
should cause an error to be thrown or not.
Coerce with duk_safe_to_string() in runtests

Previously used duk_to_string() which may cause an uncaught error when a
thrown value cannot be string coerced (e.g. an error which participates
in a prototype loop causes an error when toString() is attempted).
Improve prototype loop testcase

Should now have full coverage over internal prototype walk sites.
API documentation for duk_{get_set}_prototype()
Improve API doc for duk_push_object re: prototypes
Extend get/set prototype API testcase

Now covers undefined/object for set call, naked objects etc.
Does not cover invalid arguments to duk_set_prototype().
Release note: set/get prototype
FIXME downgrade
FIXME cleanups and downgrades
Merge branch 'api-get-set-prototype'

Add API calls duk_get_prototype() and duk_set_prototype() to allow C code to
control object prototypes directly.  The C API does not prevent prototype
loops from being formed, so it is now possible to create them.  This merge
also adds a few fixes to tolerating prototype loops in critical internal
parts like garbage collection and error throwing.