Make __proto__ a foreign callback on Object.prototype.

This moves the __proto__ property to Object.prototype and turns it into
a callback property actually present in the descriptor array as opposed
to a hack in the properties lookup. For now it still is a "magic" data
property using foreign callbacks and not an accessor property visible to
JavaScript.

The second effect of this change is that JSON.parse() no longer treats
the __proto__ property specially, it will be defined as any other data
property. Note that object literals still have their special handling.

R=rossberg@chromium.org
BUG=v8:621,v8:1949,v8:2441
TEST=mjsunit,cctest,test262

Review URL: https://codereview.chromium.org/12212011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13728 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix bogus regexp test.

The reason this test fails on ARM hardware but not on Intel hardware
(including the ARM simulator) is this:
'\xa0' is interpreted as a negative signed byte number. Casting it to
uc16 sign-extends it. The resulting string does not fit into a one-byte
string, thus a two-byte string is allocated.
For some reason the code compiled for ARM does not sign-extend, and 0xa0
fits into a one-byte string. Thus a one-byte string is allocated. Trying
to cast it to two-byte causes assertion failure.

BUG=

Review URL: https://chromiumcodereview.appspot.com/12319111

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13729 ce2b1a6d-e550-0410-aec6-3dcde31c8c00