h2o: removed a lot of semicola, make an "if not" out of an "assert". The...

h2o: removed a lot of semicola, make an "if not" out of an "assert". The function is anyway tabulated and this way we are always sure, that we are in the value of validity of the equation

mesitylene & xylene: correctly apply gaussian integration to a sensible temperature range (i.e. make 0C the reference of enthalpy) 

h2oairfluidsystem: add a . after a floating point number


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@9388 2fb0f335-1f38-0410-981e-8018bf24f1b0