[TYPO3-core] RFC: #9575: use native filter_functions for validate and sanitize

[Steffen Kamper]

Hi,

there is a different behaviour to the prior state.

As the function eg validEmail before returns false/true,
the php filter-functions return false/input string (which is that was 
the name says, it filters .-))

Most users won't discover, as 98% are testing validEmail with
if (!t3lib_div::validEmail($email)) { ... }

So 2 possibilities:
1) leave it as it is and change the phpdoc for return var
2) change return var to boolean

i would vote for 1) but i see compatibility too with 2)

vg Steffen