Initial file search implementation

See #1165.
Comment out wasteful DEBUG statements
Change "Search Books" to "Search books" for consistency with other search dialogs
Merge pull request #1189 from hwhw/master

fix strcoll() workaround
Merge pull request #1186 from Frenzie/filesearcher

Initial file search implementation
(really?) fix refresh viewport calculations

This adds more documentation about the viewport offset calculations
for refreshing rotated viewports.

The old behaviour also was (still) buggy, even after the latest round
of fixes. Now, the offsets when rotated are hopefully calculated correct.