Pacify gcc and other image rotation tweaks

Pacify gcc and other image rotation tweaks

* src/image.c: No need to include <float.h> as lisp.h does that.
(matrix3x3_copy): Remove; no longer needed.
(divide_double): New function, to avoid undefined behavior
when dividing by zero on non-IEEE hosts.
(image_set_transform): Simplify transformation computation
by avoiding the need to copy a matrix.  Pacify
gcc 9 -Wdouble-promotion and -Wmaybe-uninitialized.
Avoid unnecessary assignment of width and height.
Improve error reporting for unsupported native image rotation.