killcontext doesn't always refuse to kill an active context
newcontext(foo)$ newcontext(bar)$ is(y>0)$ killcontext(foo); -> Lisp error
sign(a+b) -> pnz or error, depending on whether a or b is declared imaginary
Fixed by commit [77d43d].
Merge branch 'master' of https://git.code.sf.net/p/maxima/code
SIGNSUM: always look at all terms of a sum, remove order dependency
assume(x > 2); is(2^x > 4) -> unknown
assume(x > 2); is(2^x > 4) -> unknown