introducing 'errors' package
table: implements errors.ErrCorrupted
journal: implements errors.ErrCorrupted
leveldb: session: implements error.ErrCorrupted
leveldb: DB.checkAndCleanFiles: implements error.ErrCorrupted
table: compaction: use cIdle cmd instead of separate 'trigger' channel
leveldb: ikey: implements error.ErrCorrupted
leveldb: removes session.version_NB method
leveldb: Batch: implements error.ErrCorrupted
iterator: strict == false now only ignore 'corruption errors'
leveldb: Batch: reuse data buffer
merge from syndtr/goleveldb