Do not clip lw when scaling dashes

Slightly change the algorithm to no longer clip the scaling factor,

thus the patterns will continue to shrink at thin line widths. If the

line width is smaller than the effective pixel size, this may result

in dashed lines turning into solid gray lines. This also required

slightly tweaking the default patterns for '--', ':', and '.-' so that

with the default line-width the final patterns would not change.

There is no way to restore the old behavior