"Intended to reduce memory usage when resharding by sharing sstable
components among shards. File descriptors are also shared from now
on, meaning that a much smaller number of file descriptors will be
used during resharding.
Fixes #1951."
branch 'excessive_memory_usage_v4' of github.com:raphaelsc/scylla
* 'excessive_memory_usage_v4' of github.com:raphaelsc/scylla:
db: avoid excessive memory usage during resharding
checked_file_impl: add support to dup
sstables: group sstable components that can be shared among shards
sstables: rename sstable member