#4992 quad_* can leave temporary variable assignments in place

[David Scherfgen]

g(u) := if u > 1.0 then throw(u) else sin(u)$
ex: funmake(g, [y[3]])$
catch( quad_qags(ex, y[3], 0, %pi) )$
y[3];  ==>  1.5707963267948966     ← an internal quadrature sample point

Spotted by Claude

[Stavros Macrakis]

I'm surprised that subscripted variables are allowed at all.

[David Scherfgen]

Fixed by commit [5e14a1].