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.
These hopefully test a reasonable set of basic, error and variations for
the twenty or so session functions. Note however that they do not
test all the session configuration settings, nor do they test anything
with register_globals enabled.
