blob: do not read data file on fill()

This will remove seeks aginst data files on read which should decrease
cache thrashing and number of IOPS.

As for records which are removed only in data file but not in index -
they will be removed automagically by datasort (defragmentation) or
manually by eblob_merge.
features: remove include hack for Mac OS X / FreeBSD

Reported by: mou@
Merge pull request #20 from SaveTheRbtz/master

Speedup internal read path, fix Darwin build