TYPO3 Core

Introduce a class to define main constants and all basic
path evaluations at an early point in bootstrap.

The patch streamlines a lot of the duplicated code for the different
entry points to TYPO3 and moves especially the path handling to a
well documented central location.

Until now, it was documented that is is possible to define own names for the
directories "typo3/", "tslib", "typo3conf/" and "t3lib/". This never
really worked without heavy core hacks and was probably never used in
production by anyone for that reason. This feature is now officially dropped.