Allow use of the pulse library for highlighting inserted item.

The pulse library provides a mechanism for fading out the highlighting
on a region which looks pretty.  This patch adds a new variable
`browse-kill-ring-highlight-inserted-item-style' which selects between
the old default style (solid) and the new fade out style (pulse).

ChangeLog

	(browse-kill-ring-highlight-inserted-item-style) New variable, the
	style to use when highlighting newly inserted items.
	(browse-kill-ring-highlight-inserted) New function, highlights the
	newly inserted item in the required style, but only if
	highlighting is turned on.
	(browse-kill-ring-insert-and-highlight) Move highlighting code out
	into `browse-kill-ring-highlight-inserted'.