Add a notice to spl_object_hash() return values comparison

[alexandre-daubois]

Fix #2406

[Girgias]

Improve wording to use the name of the === operator, but also I don't know if saying this can lead to confusing comparison needs more detail if we mention (and link) to numeric strings.

Suggested change

	Object hashes should always be strictly compared with <code>===</code> and
	<code>!==</code>, because returned hashes could be a valid integer
	representation like <code>0000000000000e600000000000000000</code> (which is
	a valid integer representation using exponent notation). Not doing so may
	lead to confusing and false comparisons.
	Object hashes should be compared for identity with <code>===</code> and
	<code>!==</code>, because the returned hash could be a
	<link linkend="language.types.numeric-strings">numeric string</link>.
	For example: <literal>0000000000000e600000000000000000</literal>.

[alexandre-daubois]

That's definitely better. It's updated, thanks for the suggestion!

[Girgias]

Thank you!