Release 1.2 2011-05-16
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Fixes for larger databases (tested up to one billion 100-byte entries,
i.e., ~100GB).

(1) Place hard limit on number of level-0 files.  This fixes errors
of the form "too many open files".

(2) Fixed memtable management.  Before the fix, a heavy write burst
could cause unbounded memory usage.

A fix for a logging bug where the reader would incorrectly complain
about corruption.

Allow public access to WriteBatch contents so that users can easily
wrap a DB.