modifications done at home, not yet incorporated MJ's objections:

modifications done at home, not yet incorporated MJ's objections:
- added buck2obj_{alloc,free}()
- extract_odes() renamed to buck2obj_convert() and simplified its interface.
  it flushes the memory pool and calls obj_new() as used e.g. in scanner.c
- attribute lengths are stored incremented s.t. 0-lengths are allowed
- the length of the compressed part is stored as U32 instead of UTF8 to allow
  0-copy compression
- temporary usage of object.c's oa_allocate removed and we call
  obj_add_attr_ref() instead of obj_add_attr()
- renamed constants BUCKET_TYPE_*
- defined internal macro RET_ERR()