Immediately purge entries from the column cache when the associated register

Immediately purge entries from the column cache when the associated register
undergoes an affinity change.  Ticket [eb5548a849].  Enhance the
SQLITE_TESTCTRL_OPTIMIZATIONS setting of sqlite3_test_control so that it
can disable the column cache for testing purposes, in an effort to prevent
future problems of a similar nature to this one.

FossilOrigin-Name: ea4e57e1c1b6663ceb12872e31a8503f6c14e3d8