don't leak streams in readFile and writeFile
don't invoke multiple callbacks when idbfs sync errors
added canOwn option to writeFile
updated idbfs sync to specify canOwn when writing to the local fs
reworked idbfs sync to use an index with openKeyCursor to avoid deserializing all values when getting the set members
Merge pull request #2080 from inolen/idbfs_updates

idbfs updates