Reapply change to with/arguments interaction.

Reapply change to with/arguments interaction.

This is svn r6415 with a bugfix.

The bug was that we can have scopes with 0 heap slots (functions with
such scopes do not need a local context) and scopes with at least
Context::MIN_CONTEXT_SLOTS.  The code generator only allocated a local
context if there were strictly more than Context::MIN_CONTEXT_SLOTS.
Before the change to with/arguments, it was impossible to actually get
a function scope with exactly Context::MIN_CONTEXT_SLOTS because every
such scope included a heap-allocated arguments (and arguments shadow)
slot.

Committed: http://code.google.com/p/v8/source/detail?r=6426

[Kevin Millikin (Chromium), 2011-01-21 10:52:40]

The bugfix I adopted was to make the FastNewContextStub include the number of
context slots in its count so we didn't subtract in the code generator and add
back in the stub.

[Mads Ager (chromium), 2011-01-21 11:02:56]

LGTM!