Merge pull request #88 from ctiller/shutdown

Makefile

include/grpc/grpc.h

src/core/surface/completion_queue.c

src/core/surface/completion_queue.h

src/core/surface/event_string.c

src/core/surface/server.c

test/core/end2end/cq_verifier.c

test/core/end2end/cq_verifier.h

test/core/end2end/gen_build_json.py

test/core/end2end/tests/graceful_server_shutdown.c