Scroll the Thumbnail of the current page into view when exiting fullscreen mode
Fix the calculation of default vertical metrics

Fixes bug 849627 and 849628.
The current code was obviously wrong per the spec 9.7.4.3.
Merge pull request #2932 from vyv03354/bug849627

Fix the calculation of default vertical metrics
Store references as pngs and write failures to separate png files.
Merge pull request #2920 from Snuffleupagus/thumbnail-on-fullscreen-close

Scroll the Thumbnail of the current page into view when exiting fullscreen mode
Merge pull request #2935 from brendandahl/png-refs2

Store references as pngs and write failures to separate png files.