speed up dc recovery as don't spend time on pickling/unpickling data and concatenate files via cat.
Change file concatenation from calling cat to python file read+write
use shutil.copyfileobj to concatinate files
Merge branch 'master' of https://github.com/reverbrain/elliptics into dc-recovery-fix-on-cat
remove extra bracket
Added option for dumping into text file all iterated keys
Switched pickle protocol to binary to reduce size of temp files and reduce processing time
Made dumping key enabled by default, to disable it introduced new option -> -u
don't add option for key dumping in dc_recovery
removed multiple context expression for python 2.6 compatibility
don't set ctx.dump_keys on dc_recovery
removed multiple context expression for python 2.6 compatibility
Merge pull request #562 from agend/dc-recovery-fix-on-cat

speed up dc recovery as don't spend time on pickling/unpickling data
Pytests: moved  fixture to global conftests. Disabled srw for test cluster in test_specific_cases. Cleaned up pytests code.
Pytests: added iterator tests.
config: use uint32_t for parsing group from config - disallow setting negative group.
bindings: added start_time and end_time methods for async_result: both for C++ and Python bindings. They returns timestamps when async result was created and finished.
Fixed calculation tnsec of elapsed_time.
python: fixed gil_guard