The sieve_binary_block_index/get() functions return NULL when the block index is
invalid somehow. This was not handled by the dumper, thereby causing a crash.

Messed up signed/unsigned characters.

Patch by Timo Sirainen.

Added the concept of a script code header to list the extensions actually used by a script (was using all extensions listed in the binary).

Properly implemented dumping a binary including a list of required extensions and support for extension-specific output.

RECOVERED FROM INCONSISTENCY: developed testsuite and binary dumping and fixed various small issues.