This change fixes a parallel make which always failed with "cannot find
-lprotobuf".

For C++ static libraries, protobuf was already added as dependency, see
commit 5383062d.

- Added ptag ignore annotation threshold
- prefixed everythig with grpc_
- removed spurious annotations in channel_create.c and client_channel.c
- removed stap_probes.h (it's generated from stap_probes.d by make)
- Updated Makefile and its template with the right way to generate stap
  probe headers from its .d definition.

This commit includes a faulty Makefile to be fixed in a follow commit.

A bunch of autogenerated variables are currently useless, because of tests actually having no source code attached to them. Let's avoid emitting useless code in that case.

variables to set up the GRPC_LATENCY_PROFILER preprocessor macro so that timing
actually takes place.

This resolves a blocker stopping a clean linuxbrew install to work with one of
the wrapped libraries.

Enables the installation of dylibs to the MacOS prefix, and ensures that the
install name of the dylibs are just their file names rather than their relative
paths from project root when built.

Adds a Makefile target called 'test_python' that first builds grpc, then call run_tests.py to run the python tests for the current configuration.

-) You can't assume bash is installed. Scripts needs to be cleaned out of bashisms.
-) You can't assume python is in /usr/bin. Use env instead.
-) AF_INET is in sys/socket.h
-) Added port_platform's basic structure for FreeBSD, based off Darwin.
-) FreeBSD doesn't have and doesn't need libdl for OpenSSL.

Not all systems are equal, and have gcc. However, cc and c++ are more common aliases for the system's compiler.
FreeBSD is an example.

Trying to make the MacOS experience better by removing various spurious messages, and increasing coverage of library paths.