q2/builtins: make efficient
dispatch: added SharedDispatcher

populate_dispatch must never use a RefDispatcher -- only a
SharedDispatcher!
q2: now builds
q2: works and tested on 2 nodes
q4: compiles
Inline peer_aggs accumulation in q2.
q4: working and fast
q2: clear input data for reduced memory usage
Merge branch 'master' into focus/queries
q3: decrease mem footprint, use new dispatchers
q2: remove string overhead
q2: Fixed buildq2: Fixed build
q2: fix double free
q3: changed to use Str instead of string
Make q1 compile
Merge branch 'focus/queries' of https://github.com/DaMSL/K3-Core into focus/queries
Fix segfault in Q3 when no join-result is available.

Fold1 on an empty collection is a _bad_ idea.
Standardize input file names
Engine logging. Q3 num_peers
builtins: more solid implementation of Str, now()