Ruby: Fix mutable backtrace
Merge pull request #1846 from nviennot/rb_fix_mutable_backtrace

Ruby: Fix mutable backtrace
Revert "Ruby: Fix ruby reconnect/close"

This reverts commit 63b455d56a10a6c0f5e37aa73a2f567f2d5b72aa.
Merge pull request #1848 from nviennot/interrupt_null

Fix crash when ctrl+c twice
Fix crash when ctrl+c twice
Merge branch 'next' into sam_alt
Merge branch 'sam_alt' into sam_alt_snap
fixed ref_count_ incrementing when adding child of many parents.
Made refcounting of snapshot_node_ pointees even _more_ correct!
Wrapped some debugfs in ALT_DEBUG in alt.cc (from previous commit).
New incremental LBA garbage collector. This commit still has some debug printfs and shutting down is not safe yet.
Put some debugfs into MemcachedBackfill.Backfill.
Merge branch 'sam_memcached_debugs' into sam_alt_snap
Fixed shut-down with new LBA GC.
fixed replace regression
Small cleanup.
added tests
Removed debug printfs
Cleaned up arguments. Also cache IO priorities were way off.
Sync LBA while GCing the LBA, so we don't end up having a very long sync which would block metablock writes.