Intermediate fix for :preselect with visual-line-mode
* swiper.el (swiper--ivy): Use `beginning-of-visual-line' and
`end-of-visual-line'. This should fix the preselect problem for
non-duplicate buffer lines.
For duplicate buffer lines, a `visual-line-number-at-pos' function is
necessary. I don't currently know how to implement such a function in an
efficient way. The naive implementation could be pretty inefficient,
comparable to doubling `swiper' startup time with `visual-line-mode'.