power precedence in printlatex #143

Hi! First of all, this is an amazing library. Thanks for your work.

I'm here to report a possible issue. When I run printlatex((a*b)^(2/3)) I should get \sqrt[3]{a^2b^2} or \sqrt[3]{(ab)^2} but I get \sqrt[3]{ab^2}. Is this an issue or am I missing something?