Fix compiler error: "a class-key must be used when declaring a friend"

google/protobuf/map_test.cc:88:16: error: expected ‘;’ at end of member declaration
google/protobuf/map_test.cc:88:18: error: ‘override’ does not name a type
.

Make .gitignore more robust

Don't rely on non-standard 'INT32_MAX' / 'INT32_MIN'.

Ignore generated test scaffolding files.

Exclude Python build artifacts.

Incorporates feedback from @xfxyjwf:
https://github.com/google/protobuf/pull/84#discussion_r20474781.

Define safe constants to use when padding enums.

Fixes #80.

Add AIX/POWER atomicops and fix compilation with IBM xlC C++ compiler.

- `int64` typedef collision with `sys/inttypes.h`
- `xlC` complains about `int` and pointer comparisons without casts

Conflicts:
	src/google/protobuf/compiler/java/java_file.cc

setup.py fixes for Python 3

Silence -Wsign-compare warning on Mac

Fixed Unused Parameter warning in headers.

Change references to `vector` to use `std::vector`

There is an example at the top of the page which contains code that appears to show a user how to create and serialize a message to a file. However the flags to open the file lack the O_CREAT flag which allows creating the file if it doesn't exist. I was troubleshooting a situation where this snippet was used and compiled, but never created a file.

Upstreaming patch used by Chromium in
https://codereview.chromium.org/693773003/

Includes files generated by each of:
   * autogen.sh
   * configure
   * make

Temporary change until a py3k-compatible google-apputils is released.