Backport PHP 7.1 fixes

[johnbillion]

In #37071, two fixes were made for issues related to PHP 7.1. The most visible is [37697] which avoids a fatal error when trying to log in, meaning users are unable to access the admin area.

[37697] and [37720] should be backported so that, at a minimum, users can at least log in to pre-4.6 installations when running PHP 7.1+.

Let's backport this to as many previous releases as possible where those two changesets apply cleanly. A separate patch should be created for each branch.

[ayeshrajans]

Changeset 37697 backport for 4.5 branch

[ayeshrajans]

Changeset 37720 backport for branch 4.5

[ayeshrajans]

Changesets 37720 and 37697 backport for 4.5 branch, combined patch

[ayeshrajans]

Changeset 37697 backport for 4.4 branch

[ayeshrajans]

Changeset 37720 backport for branch 4.4

[ayeshrajans]

Changesets 37720 and 37697 backport for 4.4 branch, combined patch

[ayeshrajans]

Attached patches for 4.4 and 4.5 branches.
For each branch, I attached separate patches for each changeset, and one combined patch of those two.

I tested the same patch up to 4.1, and they do apply with only minor offsets.

[DrewAPicture]

Assigning ownership to mark the good-first-bug as "claimed".

[johnbillion]

In 41128:

General: Backport PHP 7.1 fixes to the 4.5 branch to avoid fatal errors and warnings.

Props simonvik, ayeshrajans

See #41135

[johnbillion]

In 41129:

General: Backport PHP 7.1 fixes to the 4.4 branch to avoid fatal errors and warnings.

See #41135