Add faulterl to rebar.config, add generic_qc_fsm.erl
Add example usage instructions for fault injection library 'faulterl'
Handle lock errors better (e.g. ENOSPC)

Fixes include these slightly larger patches:

* reshuffle to avoid var binding shadows
* restrict pattern match to throw exception to catch at caller
Robustify failed writes, including when tombstone write fails
Robustify failed merges

Including:

* list_data_files() fails
* Fix file-scan exceptions in merge()
* Fix EUnit bitcask:merge_test()
* Partial merge check should be after file opens fail/succeed
Introduce error_msg_perhaps() to avoid log spam when TESTing

Also, add minor '_ = ' pattern match to make Dialyzer happier
Remove debugging cruft
Merge pull request #161 from basho/slf-faulterl-introduction2

Fixes for 'faulterl'-style fault injection

Reviewed-by: evanmcc