SQLite

** one or more tables. Operations on a single table are grouped together,
** but may occur in any order (i.e. deletes, updates and inserts are all
** mixed together).
**
** Each group of changes begins with a table header:
**
**   1 byte: Constant 0x54 (capital 'T')
**   Varint: Number of columns in the table.
**   nCol bytes: 0x01 for PK columns, 0x00 otherwise.
**   N bytes: Unqualified table name (encoded using UTF-8). Nul-terminated.
**
** Followed by one or more changes to the table.
**
**   1 byte: Either SQLITE_INSERT, UPDATE or DELETE.
**   1 byte: The "indirect-change" flag.
**   old.* record: (delete and update only)
**   new.* record: (insert and update only)
**
** The "old.*" and "new.*" records, if present, are N field records in the
** format described above under "RECORD FORMAT", where N is the number of
** columns in the table. The i'th field of each record is associated with
** the i'th column of the table, counting from left to right in the order
** in which columns were declared in the CREATE TABLE statement.
**
** The new.* record that is part of each INSERT change contains the values
** that make up the new row. Similarly, the old.* record that is part of each
** DELETE change contains the values that made up the row that was deleted 
** from the database. In the changeset format, the records that are part
** of INSERT or DELETE changes never contain any undefined (type byte 0x00)
** fields.
**
** Within the old.* record associated with an UPDATE change, all fields
** associated with table columns that are not PRIMARY KEY columns and are
** not modified by the UPDATE change are set to "undefined". Other fields
** are set to the values that made up the row before the UPDATE that the
** change records took place. Within the new.* record, fields associated 
** with table columns modified by the UPDATE change contain the new 
** values. Fields associated with table columns that are not modified
** are set to "undefined".
**
** PATCHSET FORMAT:
**
** A patchset is also a collection of changes. It is similar to a changeset,
** but leaves undefined those fields that are not useful if no conflict
** resolution is required when applying the changeset.
**
** Each group of changes begins with a table header:
**
**   1 byte: Constant 0x50 (capital 'P')
**   Varint: Number of columns in the table.
**   nCol bytes: 0x01 for PK columns, 0x00 otherwise.
**   N bytes: Unqualified table name (encoded using UTF-8). Nul-terminated.
**
** Followed by one or more changes to the table.
**
**   1 byte: Either SQLITE_INSERT, UPDATE or DELETE.
**   1 byte: The "indirect-change" flag.
**   single record: (PK fields for DELETE, PK and modified fields for UPDATE,
**                   full record for INSERT).
**
** As in the changeset format, each field of the single record that is part
** of a patchset change is associated with the correspondingly positioned
** table column, counting from left to right within the CREATE TABLE 
** statement.
**
** For a DELETE change, all fields within the record except those associated
** with PRIMARY KEY columns are set to "undefined". The PRIMARY KEY fields
** contain the values identifying the row to delete.
**
** For an UPDATE change, all fields except those associated with PRIMARY KEY
** columns and columns that are modified by the UPDATE are set to "undefined".
** PRIMARY KEY fields contain the values identifying the table row to update,
** and fields associated with modified columns contain the new column values.
**
** The records associated with INSERT changes are in the same format as for
** changesets. It is not possible for a record associated with an INSERT
** change to contain a field set to "undefined".
*/

/*
** For each row modified during a session, there exists a single instance of
** this structure stored in a SessionTable.aChange[] hash table.
*/
struct SessionChange {