[TYPO3-core] RFC #13418: Allow t3lib_div::_GETset() to set specified key

[Benjamin Mack]

Hey Felix,

nice one. Two things that came to my mind when reading the patch:

  * As there is already a use-case, could you provide a unit test for it 
as well?

  * Could you please describe the new behaviour inside the header 
comment of the method; and update your patch accordingly?

Thank you!

All the best,
Benni.