New build uploaded at:
http://download.calibre-ebook.com/betas/
Fixes:
1) Fix deleting books failing on some windows machines
2) Improve rendering speed of the cover grid when scrolling using the slider in the scroll bar or the mouse wheel by not rendering intermediate covers between the start and end point.
3) Show authors in addition to title for books that have no cover in the grid view
4) Make the spacing between covers in the grid view configurable
5) Fix search highlighting not working in the grid view
6) Fix true/false searches on numeric columns
7) Fix errors when merging books that have the same tag