add keydir_trim_fstats to bitcask_nifs, allowing the post merge live
files update to remove entries for deleted files so they are no longer
considered for merge or for status
lazily create merge files to avoid creation of empty files
actually, um, iterate over the list
Fix bitcask_qc_expiry.erl model: don't expect merge if 100% of ops are deletes
Merge pull request #115 from basho/refactor/pevm-lazy-mergefile-create

lazily create merge files to avoid creation of empty files
- add stats return for non-existent fstats entries
- log when non-existent fstats entries are trimmed
- dedup the fstats list so the above logging isn't constantly
  triggered.
Merge pull request #116 from basho/bugfix/pevm-fix-resource-leak

Fix fstat struct leak.
Merge branch 'develop' into refactor/pevm-avoid-file-server

doing this to bring the branch up to date and fix a known merge
issue w/ PR #115