BK-420: Unset environment variables set by Xvfb
OB-42: fixed missing 'alt' attribute for images (epub)
OB-42: filter image attributes (epub)
OB-73: default values for mode and license.
OB-74: RequestError is now pickable
OB-75: allow custom license values
Removed the cgi-bin directory.
Merge branch 'devel' into bookjs