[FEATURE] Add "auto" absRefPrefix option

For automatic distribution configuration
like the introduction package, a dynamic
option to find out whether TYPO3 is installed
under "/" or "/mysite/" the TypoScript
option config.absRefPrefix = auto
calculates the absRefPrefix automatically.

Releases: master
Resolves: #58366
Change-Id: Ia0d335665c9b30d21b886c8e9ac4c1ccdb069adc
Reviewed-on: http://review.typo3.org/29747
Reviewed-by: Stefan Froemken <froemken@gmail.com>
Reviewed-by: Benjamin Kott <info@bk2k.info>
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>