Slight bug fixes:

* cot(0), coth(0), cotd(0) now returns NAN rather than throwing a DivisionByZero error
* Handling of ^ in Evaluator tweaked so that e^x and exp(x) always returns the same value. (Apparantly, pow(M_E,x) and exp(x) in PHP are not quite identical.)
* Bug in LaTeXPrinter was causing a missing \cdot in some expressions, e.g. "2*3^2" was written as "23^2" rather than "2\cdot 3^2". This is now fixed.