The sqlite3KeyInfoOfIndex() routine ([/artifact/67bb05b1077?ln=4192,4199|here])
can return a stale KeyInfo object in shared cache mode.  

Scenario:

  *  Two open database connections (A and B) on the same cache
  *  The shared pIdx object is holding a KeyInfo object for A
  *  Connection A closes.
  *  Connection C opens, and by (bad) luck is allocated
     the same database connection pointer as A had.
  *  Connection C now tries to get a KeyInfo object for index pIdx but
     is handed the stale one from A.  The KeyInfo object itself is ref-counted
     and so it is still live.  But the KeyInfo points to CollSeq objects
     within the old A connection that are now dead and have been freed.

This problem appears to have been introduced by check-in [c80e229dd9c1230ab]
on 2013-11-07, which first appeared in SQLite version 3.8.2.