#2483 function polarform has bug

[Valery Lovchikov]

(%i1) polarform(f^^(1/2));
(%o1) %e^(%i*atan2(imagpart(f^^(1/2)),realpart(f^^(1/2))))*sqrt(realpart(f^^(1/2))^2+imagpart(f^^(1/2))^2)

but
(%i2) polarform(sqrt(f));
(%o2) sqrt(f)

build_info("5.28.0-2","2012-08-27 23:16:48","i686-pc-mingw32","GNU Common Lisp (GCL)","GCL 2.6.8")