#2260 ratsubst() causes stack overflow

[Anton Voropaev]

INPUT

build_info();
ratsubst(x,sqrt(log(2)),sqrt(log(2))), radsubstflag = true;

INPUT AND OUTPUT

(%i1) build_info();
Maxima version: 5.25.0
Maxima build date: 12:0 8/2/2011
Host type: i686-pc-mingw32
Lisp implementation type: Clozure Common Lisp
Lisp implementation version: Version 1.7-r14925M (WindowsX8632)
(%o1)
(%i2) ratsubst(x,sqrt(log(2)),sqrt(log(2))), radsubstflag = true;
Maxima encountered a Lisp error:
Stack overflow on value stack.
Automatically continuing.
To enable the Lisp debugger set *debugger-hook* to nil.