Add a facility to control tracing without recompiling

Makefile

build.json

src/core/channel/channel_stack.h

src/core/debug/trace.c

src/core/debug/trace.h

src/core/iomgr/tcp_posix.c

src/core/security/secure_endpoint.c

src/core/surface/init.c

src/core/surface/surface_trace.h

vsprojects/vs2013/grpc.vcxproj

vsprojects/vs2013/grpc.vcxproj.filters

vsprojects/vs2013/grpc_shared.vcxproj

vsprojects/vs2013/grpc_shared.vcxproj.filters

vsprojects/vs2013/grpc_unsecure.vcxproj

vsprojects/vs2013/grpc_unsecure.vcxproj.filters