Packfile API cleanup: rename Parrot_readbc to Parrot_read_pbc, _loadbc => _load_pbc

[rurban]

Attached is a patch which:

- renames Parrot_readbc to Parrot_pbc_read (as heard on IRC)
- renames Parrot_loadbc to Parrot_pbc_load
- adds a third debug argument to Parrot_pbc_read which is stored in

the returned pf->options member, to be able to react in parrot and in other pbc utils differently.
Used for debugging pbc transformers.

- macrofy TRACE_PACKFILE printing (debug levels 1, 2 and 3)

Rationale: Debugging the pbc reader requires rebuilding libparrot and pdump, but this affects parrot also. parrot should not debug-print pbc transformers while testing. 64-bit pbc unpacking has still broken alignments, 64bit BE and 12-byte floats are untested, so there's still a way to go with this debugging stuff.

Also included is the TT #258 TODO patch "pcb_disassemble options -[bho?], enable roundtrips". I can apply them seperately.

The patch needs a reviewer.

[particle]

close, but the naming convention is to put the subsystem first, so the functions should be named like Parrot_pbc_{read,load} instead.

~jerry