[TYPO3-core] RFC: #15786: Set readLLPHPfile to deprecated, resolve undefined vars in t3lib_div

[Benjamin Mack]

Hey Steffen,

now that I think of it, you should do it this way:

 * This patch should set the t3lib_div::readLLPHPfile() deprecated, and
change all the occurences of locallang.php references to xml

 * The unrelated initialization cleanup should go as a followup to #15799.

Thanks.
Benni.