Use identity operator (===) instead of equality (==) where appropriate

Uh, patch was null bytes, that's why it did pass the tests :)

Let's take small steps:

• Move JavaScript changes to a separate issue #2354653: (JavaScript) Use identity operator (===) instead of equality (==) where appropriate.
• Only change those occurrences where the right side is known to be either a string or an array.

Converted some more occurrences, those are mainly in test-code.

For reference, use the following grep to locate the remaining occurrences. They mostly are found in function/methods copied over from core. Also some of them are integer constant on the right side which should be safer than string.

find * -type f -not -name '*.api.php' -not -name '*.js' -not -name '*.vcl' -not -name '*.vtc' -not -name '*.txt' -not -name 'Makefile' | xargs git grep '[^=!][=!]=[^=!]'