Use isinf and isnan from std::, to avoid ambiguities

[[Imported from SVN: r12435]]

dune/solvers/solvers/tcgsolver.cc

@@ -235,7 +235,7 @@ void TruncatedCGSolver<MatrixType, VectorType>::solve()
 
         normOfOldCorrection = normOfCorrection;
 
-        if (!isinf(convRate) && !isnan(convRate)) {
+        if (!std::isinf(convRate) && !std::isnan(convRate)) {
             totalConvRate *= convRate;
             this->maxTotalConvRate_ = std::max(this->maxTotalConvRate_, std::pow(totalConvRate, 1/((double)convRateCounter+1)));
             convRateCounter++;