Bug fix: allow querying the "leveldb.num-files-at-level<n>" property

The DB.GetProperty() erroneously used fmt.Scanf() instead of
fmt.Sscanf() when trying to parse the level in properties of the form
"leveldb.num-files-at-level<n>".  This commit changes the method
to use fmt.Sscanf() instead, and adds a test case to check for the
presence of the problem.
Merge pull request #79 from seehuhn/master

Bug fix: allow querying the "leveldb.num-files-at-level<n>" property
util: BufferPool.Put should't do nothing instead of panic'ing after pool been closed
leveldb: fixes compaction cmd that might be stuck if compaction transaction error for extended period
table: Don't embed Reader in the block

The Reader might be released before block does; when this happen the the block will
refer to an invalid Reader instance.

This fixes bug introduced by 546b03ad0e07c6b711ef3f99aa79045bc20194b0 and fixes #72.
Revert "leveldb: Trap for issue #72"

This reverts commit c4f1f5a18485e99337a746c5b21b1e9f5f286a2d.
testing: allows using custom tempdir
leveldb: combined testing for issue #72 and #83
leveldb: sets all merged iterator strict parameter to true

Prevent silent error; issue #83.
opt: makes StrictIterator default #83
leveldb: introducing Batch.Dump, Batch.Load and Batch.Replay methods (closes #85)
leveldb: introducing Batch.Len method
Merge remote-tracking branch 'upstream/master'