The existing implementation was causing segmentation fault because
src/ruby/ext/grpc/rb_call.c:358 was trying to convert any value type other than
Array to String. The Array type is handled in first `if`. This change will cause
the Ruby code that sends non-string values to fail with a better message:
`ArgumentError: Header values must be of type string or array`

Better message for on_connect error

Remove year range requirement for copyright checker

Fix the unix socket #ifdef in init.c

Optionalize load balancing policies

Upmerge

Conflicts:
	Makefile
	build.yaml
	package.json
	src/core/lib/surface/version.c
	src/csharp/Grpc.Core/VersionInfo.cs
	src/csharp/build_packages.bat
	src/python/grpcio/grpc_version.py
	src/ruby/lib/grpc/version.rb
	tools/doxygen/Doxyfile.c++
	tools/doxygen/Doxyfile.c++.internal
	tools/doxygen/Doxyfile.core
	tools/doxygen/Doxyfile.core.internal

The release-0_13 branch is now 0.13.2-pre1.

Idempotent request support for core

Introduce byte counting to the transport API

Initial canaries for downstream merges

Flagging the 0.13.1 release.

Add python script for running performance tests

0.13 a tiny upmerge 

Don't allow precompiled binaries in tests

Refactor C# building in run_tests.py (revert a revert)

Add script to create interop worker

Revert "Refactor C# building in run_tests.py"

Revert "added grpclb support to sockaddr resolver"

Manual upmerge from 0.13