Merge pull request #1320 from chrox/master

fix filemanager cannot remember sorting order
only open frontlight device on Kobo devices that actually have light
Merge pull request #1323 from hwhw/master

only open frontlight device on Kobo devices that actually have light
Fix #1299
Merge pull request #1324 from variousvirgil/patch-1

Fix #1299
wrap computation intensive functions in hook free env when makeing coverage test
so that Travis CI job won't fail because of timeout.