Fix mma free algorithm when no answer

[kcrisman]

The output from page in the code for

(exp(3*x)/cosh(exp(x))).integral(x,algorithm='mathematica_free')

is

"inputForm"class="hidepod"><hr/><p><p><i>Mathematica</i>couldnotfindaformulaforyourintegral.Mostlikelythismeansthatnoformulaexists.[<ahref="http://reference.wolfram.com/mathematica/tutorial/IntegralsThatCanAndCannotBeDone.html"target="_blank">Moreinformation</a>]</p></p><hr/></div><divid=

So we probably just need to parse for that and return an appropriate error.

See this ask.sagemath question.

CC: @slel

Component: calculus

Issue created by migration from https://trac.sagemath.org/ticket/19046