Updates to the sqlite3_analyzer utility:  Change the names of some labels,
especially change "Fragmentation" to "Non-sequential pages".  Revise the
computation of non-sequential pages so that it ignores itercalated non-leaf
pages (overflow and index pages).
In the nextchar.c extension, allow the second argument to the next_char()
function to be a subquery.
Add new test file fts3defer3.test.
Fix typo in comment.  No changes to code.