iteration: checks ranges on iteration even if index isn't sorted. Use bsearch for checking if the key from ranges.
stress: added tests for iteration: out of ranges, part of ranges and full range.
Fixed typo. Extended comments.
stats: updates total size of blobs on write_prepare.
eblob_check_free_space use this stat for determining that blob_size_limit is reached.
Merge pull request #95 from shaitan/stress

Added iteration tests to eblob stress.