Increase the default minimum PMA size for multi-threaded sorting from 10x
the page size to 250x the page size.  Provide the SQLITE_SORTER_PMASZ
compile-time option to change this default.
Add the SQLITE_REVERSE_UNORDERED_SELECTS compile-time option that causes the
"PRAGMA reverse_unordered_selects" setting to be on by default.
Make the sqlite3_table_column_metadata() interface available by default and
without requiring the SQLITE_ENABLE_COLUMN_METADATA compile-time option.
Other sqlite3_column_* interfaces that have a run-time penalty even if they
are unused still require the SQLITE_ENABLE_COLUMN_METADATA option at
compile-time.
Lower the default SQLITE_SORTER_PMASZ value back to 10, where it has been for
the past couple of releases.  Applications that need a larger value can set
one.
Add extra tests to e_walckpt.test.
Fix the sqlite3_table_column_metadata() routine so that it gives the correct
answer for the "rowid" column in a WITHOUT ROWID table.  Enhance it so that
it can be used to check for the existence of a table by setting the column
name parameter to NULL.  The routine is now included in the build by
default, even without the SQLITE_ENABLE_COLUMN_METADATA compile-time option.
Fix typos in the documentation for sqlite3_table_column_metadata().
No changes to code.