bug#13000: 24.2.90; underwave doesn't look as good as other IDEs

[Leo]

Thanks to Aurelien Aptel for implementing this feature. I have started
using it in flymake to indicate errors. However, I have noticed that it
doesn't look as good as that of, for example, the pycharm IDE. Here is a
screenshot comparison.

pycharm-wave.png
Description: pycharm-wave.png

emacs-wave.png
Description: emacs-wave.png

In the IDE the wave line is thinner and the ripple bigger. So it appears
clearly wave-like. In emacs, it looks too similar to a blurry straight
line.

Leo