Further simplify the mmallocs, and improve its introspection abilities
- Ensure that the mmallocation code will never return NULL (but die
verbosely), and simplify the using code accordingly.
- Stop using THROWF in there, because these functions probably need
malloc to work, and that what broke when we want to issue a message.
Use printf/abort instead.
- Introduce a SMALLEST_POSSIBLE_MALLOC. It already existed (and were
defined to sizeof(struct list) to ensure that free fragments can be
enlisted, but I need this to declare the block metadata
- Add a frag_size information within the bloc info structure. It may
not perfectly be kept uptodate yet (in particular, by realloc)
