Improved little endian byte order detection

Including <sys/param.h> on Mac/iOS doesn't define __BYTE_ORDER so
PROTOBUF_LITTLE_ENDIAN was never being defined. This commit adds a check
for the __LITTLE_ENDIAN__ macro which is defined by clang and Apple gcc on
little endian architectures.

Support Ruby code generation only for proto3.

Update Ruby build setup to produce gems successfully. Include upb as a single .c / .h file.

system. The Ruby module build now uses an amalgamated distribution of
upb, and successfully builds a Ruby gem called 'google-protobuf' with
module 'google/protobuf'.

Source code refactoring. Extracted common functionality in cpp_helpers.c...

Returned print_indent and print_outdent back to printservicestub and printserviceclass in python generator

Make C++ code generation of string oneof field compatible with C++11

Conflicts:
	configure.ac

Source code refactoring. Extracted common functionality in cpp_helpers.cc and python/python_generator.cc

Provide a Ruby extension.

This adds a Ruby extension in ruby/ that is based on the 'upb' library
(now included as a submodule), and adds support for Ruby code generation
to the protoc compiler.

Ignore artifacts from autogen.sh

language.

tests with macro PROTOBUF_HAS_DEATH_TEST.