db/schema_tables: Consider differing dropped columns
db/schema_tables: Consider differing dropped columns

If a node is notified of a schema change where the schema's dropped
columns have changes, that node will miss the changes to the dropped
columns. A scenario where this can happen is where a column c is
dropped, then added as a different typed, and then dropped again, with
a node n having seen the first drop and being notified of the
subsequent add and drop.

Fixes #2616

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>
Message-Id: <20170725170622.4380-1-a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

duarten/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla