Backport fixes to shared-cache mode, from the shared-cache-fix branch, to
version 3.7.9
Fix an accidental fork on branch-3.7.9.
Add QNX-specific performance tweaks to the unix VFS.
Change the ICU tokenizer so that it does not attempt to call strlen(NULL).
This is a cherry-pick of the fix in [04298f1ac42c40c] on 2012-03-31 first
appearing in release 3.7.12.
Use a constant string "BINARY" for the unspecified collating sequence.
This is part of check-in [635e3a762dd] that is being back-ported.
Merge the omit-wal-fix branch into branch-3.7.9 where it belongs, and in so
doing get branch-3.7.9 working with SQLITE_OMIT_WAL.
Cherrypick [557c69055a3] and [0064bab7714] (OP_Once-related fixes for triggers).
Cherrypick [79ef8e3c77] (Apply the same restrictions on constant refactoring to statements within a trigger program as top-level statements).