core: add asserts to rwlock
core: add asserts to rwlock

Purpose of these asserts is to catch a possible misuse of rwlock.
For example, if rwlock::write_unlock() is called twice, there would
be an overflow in the semaphore used by rwlock. That would be hard
to debug.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>
Message-Id: <1457807576-8015-1-git-send-email-1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

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