Added missing but included headers to build.json

Introduced compression levels as an abstraction for the actual algorithm

Disallow started request writers on GRPCCall init

Prints test names as ruby tests run

make sure docker image is up-to-date before each build

Document core behavior w.r.t. argument lifetimes

Also clean up some excess whitespace and make some notes about ownership.

Support sending and showing received metadata in grpc_cli

New core shutdown API

Link to official protobuf podspec in the README

It was still linking to my pull request's podspec.

temporary hotfix before backup poller removal is done

Transforming gRPC.podspec to use build.json instead of globbing.

Initial progress on ruby shutdown api migration

+ all tests pass,
- but there are a couple of workarounds
- tests are flaky

Various Jenkins-related tweaks.

-) created a .profile at the root of the docker image - seems the new nvm script requires that.
-) installing simplejson and mako python packages, for the sanity check.
-) calling prepare_travis.sh in order to try and download precompiled packages for openssl and protobuf.
-) using the new "config" axis.
-) improved the output of prepare_travis.sh.

Fixed file renaming in podspec template

Make warnings errors when building Python tests.

Update the Status API

Added flags support to grpc_op.

Add PHP timeout interop test