fix($timeout): `verifyNoPendingTasks()` throws even for non-timeout pending tasks

[gkalpak]

Do you want to request a feature or report a bug?

Bug

What is the current behavior?

ngMock's $timeout.verifyNoPendingTasks() throws if there are deferred tasks that are not related to $timeout.
Reproduction

What is the expected behavior?

ngMock's $timeout.verifyNoPendingTasks() should not throw if there are deferred tasks that are not related to $timeout.

What is the motivation / use case for changing the behavior?

It makes it difficult/unintuitive to test code that uses $timeout wrt pending tasks.

Which versions of Angular, and which browser / OS are affected by this issue? Did this work in previous versions of Angular? Please also test with the latest stable and snapshot (https://code.angularjs.org/snapshot/) versions.

Angular versions: 1.4 and 1.5 (those I tested with, but should affect oldrer versions too)
Browsers: All

Other information (e.g. stacktraces, related issues, suggestions how to fix)

When this method was introduced (back in f0c6ebc), $timeout was probably the only service that used $browser.defer(), so all $browser.deferredFns came from $timeout (thus an non-empty array, meant pending timeouts).
This is no longer the case. E.g. $browser.defer() is used in $evalAsync() and $applyAsync(), which means it transitively used throughout Angular (in watchers, directives etc).

[gkalpak]

This has been broken for so long, that fixing it should probably be considered a breaking change 😞