Automatically generated comments on many VDBE opcodes when in SQLITE_DEBUG
most.  Comments derive from the "Synopsis:" field added to each opcode
definition in vdbe.c.
Enhanced display of register ranges in the auxiliary comments added to EXPLAIN.
Add the SQLITE_ENABLE_EXPLAIN_COMMENTS compile-time option to enable extra
commentary in the EXPLAIN output.  Formerly, this was only available with
SQLITE_DEBUG.
Add the "Esri Spatially-Enabled Database" file format to the magic.txt file.