drop request's scriptFile checks in favour of getlastmod() built-in function

[pine3ree]

a little refactoring

• It allows us to let php do the dirty job for us (with the same result), thus removing distracting lines and properties from the persistence class (I'had never used this function before, I mean since 2001...., I stumbled upon it recently)
• dropped a few related test cases that do not apply anymore (my coveralls account still says 100% coverage)

Note:
I would have liked to test different getLastModified() return values, but: 1) I cannot find a way to mock builtin php functions return values (getlastmod, filemetime) without using pecl extensions. 2) I could mock the return value of getLastModified using an inline class, but at the expense of changing the visibility of the method to "protected".

[weierophinney]

That is such a nice find - I'd never known about that, and it was the exact functionality I was trying to create previously!

[weierophinney]

Thanks, @pine3ree!