Extra backwards-compatibility tests verify that UNIQUE and PRIMARY KEY 
indices are created in the correct order.  Other backwards-compatibility
tests already cover this, but it does not hurt to double up.
Add a procedure to handle the messy details of allocating an Index object
from the heap.
The Index object now has nKeyCol and nColumn.  nColumn is the total number
of columns and nKeyCol is the number of key columns.  Currently these always
differ by one.  Refactor aiColumn[] to be of type i16 instead of int.
Build internal data structures appropriately for WITHOUT ROWID tables.
Some simple inserts and queries working on WITHOUT ROWID tables.