#19 Decouple namespace mapping from store operations.

Namespace mapping has no business at the store level. It is an arbitrary mapping with no preservation value, and works at the term level, while stores operate at the buffer level. As long as the store normalizes all incoming URIs and stores them in their canonical form (which MUST always be), the namespace mapping can be applied to the graph and leave the store unaware of it.

This also fixes a Makefile issue that created objects without debugging symbols for make debug.