Do not bump stat data on flush or release if no data was written.
Use telltale indicator of failing to seek.
Use GErr for fill_stat_generic when lseek fails.
Log notice when setting file to zero length in the cache.
Only insert an empty entry into the stat cache on truncation.
Zero-length file stat data should get pushed on create or truncate.
Merge pull request #88 from pantheon-systems/master

Deploy mtime and zero-length file fixes