introduced BookHash table
DB class structure simplification (no statement variables, map instead)
Merge branch 'master' into ice-cream-sandwich
Merge branch 'ice-cream-sandwich' into yota2
Merge branch 'yota2' into kindle
BookHash table used for faster synchronization (we do not recompute SHA-1 hash every time)
Merge branch 'master' into ice-cream-sandwich
Merge branch 'ice-cream-sandwich' into yota2
Merge branch 'yota2' into kindle