Fix name conflict bug in zero rad

fix variable creation issue  in pimdec::zeroRad, line 3782.
Variable access is done by var(i) as suggested.

Test with
Tst/Short/bug_name_conflict_in_zeroRad.tst

Introduces a new method getNewVariableName() in ringutils.lib to get a conflict-free variable name.
For making this possible,
a couple of new documented and teste procedures were introduced:

Listutils::extendList
Stringutils::splitString
Stringutils::assembleStringArray
Ringutils::getNewVariableName
Ringutils::getNewRingVariableName

Jakob