Unofficial tag - do not use

main: single BeesContext instance per process

After weeks of testing I copied part of a change to main without copying
the rest of the change, leading to an immediate segfault on startup.

So here is the rest of the change:  limit the number of
BeesContexts per process to 1.  This change was discussed at
https://github.com/Zygo/bees/issues/54#issuecomment-360332529 but there
are more reasons to do it now:  the candidates to replace the current
hash table format are less forgiving of sharing hash tables, and it may
even become necessary to have more than one hash table per BeesContext
instance (e.g. to keep datasum and nodatasum data separate).

Signed-off-by: Zygo Blaxell <[email protected]>