Scaffold flag bit 3 now indicates that there is a big table. This means that
the table size at the start of the table is a 32-bit value, and if bpp = 0,
then scaffold index entries are 32-bit.

For backwards compatibility, large tables should not be used when there is
<64K of table data. Indeed, for bitmap files, which only need 8 bytes of
table data, large data tables are not supported.

When big tables are in use, bit 0 of the scaffold flags (all scaffold base
chars are 16-bit) should be clear.

In a big scaffold table, the entries are:

    ns x 4 - 4    offsets to scaffold data (32-bit)
                  bits 0-23 = offset of scaffold data from table start
                  bits 24-29 reserved (must be zero)
                  bit 30 => scaffold data has no base - first 3 bytes of
                            scaffold data are omitted and treated as zero.
                            bit 31 should be clear.
                  bit 31 => base character code is 2 bytes, else 1 byte


In addition, the Font Manager now supports dependencies on any chunk.