Remove ENTER_V8 from small API functions that do not need access to

V8's heap or only need read access.

This means that IsDeadCeck and EnsureInitialized could sometimes be
called without having already entered the VM.  To simplify things,
this is made always the case.  A couple of error callbacks do not need
to leave V8 because they haven't entered.

Consistently enter V8 after LOG_API (since LOG_API is sometimes before
EnsureInitialized or IsDeadCheck).

This all should have no effect unless V8 is built with
ENABLE_HEAP_PROTECTION and run with --protect-heap.

Review URL: http://codereview.chromium.org/56211

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1672 ce2b1a6d-e550-0410-aec6-3dcde31c8c00