A few more C API functions.
Merge pull request #90 from alberts/morecapi

A few more C API functions.
expose wal_dir in db_bench

Summary: as title

Test Plan: ran db_bench

Reviewers: dhruba, haobo

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16269
Schedule flush when waiting on flush

Summary:
This will also help with avoiding the deadlock. If a flush failed and we're waiting for a memtable to be flushed, we should schedule a new flush and hope a new one succeedes.

If paranoid_checks = false, Wait() will still hang on ENOSPC, but at least it will automatically continue when the space frees up. Current behavior both hangs and deadlocks.

Also, I renamed some 'compaction' to 'flush'. 'compaction' was leveldb way of saying things.

Test Plan: make check

Reviewers: dhruba, haobo, ljin

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16281
Merge branch 'master' into columnfamilies