Don't expose references in debug_backtrace() or exception traces.
This is regardless of whether the argument is by-reference or not.
As a side-effect of this change, exception traces may now acquire
the interior value of a reference, which may be unexpected for
some internal functions. This is what necessitated the change in
the spl_array sort implementation.
The only case here that might be *somewhat* sensible is the userdata
argument of array_walk(), which could be used to keep persistent state
between callback invokations -- with the WTF moment that the final
result after the walk finishes will be unchanged. Nowdays, this is
much better achieved using a closure with a use-by-reference.
PHP requires boolean typehints to be written "bool" and disallows
"boolean" as an alias. This changes the error messages to match
the actual type name and avoids confusing messages like "must be
of type boolean, boolean given".
This a followup to ce1d69a1f6, which
implements the same change for integer->int.
