Remove bad checkCast from DWRF long stream
Improve unknown value stream error message
Fix ORC map writer for null keys

Map entries with a null key are ignored (not rendered)
Reset in-dictionary stream when opening the stripe or row group
Reset slice dictionary stream for safety
Fix BooleanStream skip bugs

Adjust data byte when skipping bits
Fix skip to end of stream
Add toString to OrcInputStream
Add ORC checkpoints

Only flush buffered values if necessary