Fix Bug#16183 about `global-hl-line-sticky-flag'.

Fix Bug#16183 about `global-hl-line-sticky-flag'.

* hl-line.el (global-hl-line-overlay): Make a local variable.
(global-hl-line-overlays): New variable to store all overlays.
(global-hl-line-mode): Don't delete overlays from the current
buffer when `global-hl-line-sticky-flag' is non-nil.
(global-hl-line-highlight): Add new overlays to
`global-hl-line-overlays'.
(global-hl-line-unhighlight-all): New function to delete all
overlays when turning off `global-hl-line-mode'.