Stash merged
Remove ipdb
datasets uses discover, not .dshape
route to communicate expresions via pickle strings
server: full expr api
Expr: add leaves method to Expr
expr: implement leaves on merge and union
expr: leaves work on scalars too
compute: V compute down/up pattern
Remove to_json
server: ExprClient
Test for summary
Use dispatch for tree serial/deserial
Remnants of to_json
Keep as a list
Use fixtures for summary test
Give test a proper name
Merge branch 'server-exprs' of github.com:cpcloud/blaze into server-exprs

Conflicts:
	blaze/expr/tests/test_table.py
compute: V fails gracefully on missing leaves
server: ExprClient raises error on server issue