TYPO3 Core

Problem:
1) The marker handling functions in t3lib_parsehtml are often called staticaly although there're not declared static (even is the case within t3lib_parsehtml itself).
According to http://ilia.ws/files/ez_performance.pdf this results in a drop of performance, other than that it produces notices or warnings and it is not good in general of course.

2) There's an inconsistency: although a method substituteMarkerArray() exists, there's no substituteSubpartArray()

Solution:
1) Declare those methods static
2) introduce the missing method substituteSubpartArray()

Notice:
There's also some cleanup in t3lib_parsehtml and tslib_content. No functionality has been changed except for the addition of the new method in t3lib_parsehtml

(issue imported from #M9283)