[TYPO3-50-general] strict separation of libraries and extensions

[Martin Kutschker]

Hi!

Currently t3lib is a mess as it sometimes checks BE and FE modes (mostly 
for charset stuff). In other places BE code happily executes special code 
for certain extensions (mostly old list code for old tt_ extensions).

To me this is bad style. If it's not in the guidelines already I suggest to 
add a section about code separation that goes beyond a mere capsulation of 
classes.

Masi