Add NetBSD support.
It works fine under NetBSD/amd64 6.99.47.
Prepared load (-l N) support for windows.

Inspired by:
http://stackoverflow.com/questions/23143693/retrieving-cpu-load-percent-total-in-windows-with-c
Fixed/improved -l N documentation For windows

On windows "system load" is not so obvious term, added line explaining N
argument in -l N
Fixes for windows CalculateProcessorLoad

- Fixed bad logic condition,
- Added comment to clarify
Small usage info fix for windows
Improved load calculation

Added code to gracefully handle:
1. Call to CalculateProcessorLoad with not incremented ticks (fast calls
to GetSystemTimes can result same results),
2. Smooth/filter load estimation for consecutive calls.
Merge pull request #799 from ryo-on/netbsd-support

Add NetBSD support.
Fixed naming convention in GetLoadAverage support functions.
Changed implementation to provide load from 0 to ProcessorCount

This makes this implementation more consisten with POSIX load avarage.
Remove extra info from Usage()

As now behavior is similar on on platforms, this can probably be removed
Merge pull request #798 from kwesolowski/master

Provided Basic Support for -l N option on windows platform.
add some parens to silence a gcc warning
amend HACKING.md with instructions for Arch Linux
Merge pull request #802 from martine/parens

add some parens to silence a gcc warning
Merge pull request #803 from martine/arch

amend HACKING.md with instructions for Arch Linux
Provide an error message on malformed lets. Fixes #807.
Merge pull request #808 from nico/bettererror

Provide an error message on malformed lets. Fixes #807.
Use a small, standalone testing framework instead of googletest.

Ninja currently uses googletest for testing. That makes building
ninja_test somewhat annoying since it requires that one passes
--with-gtest PATH to configure. It turns out just implementing the bits
of googletest that ninja uses needs about the same amount of code than
making the --with-gtest flag in configure.py work and making googletest
print test results in a way we want (!)

In addition to making configuration simpler, this also makes compiling
tests much faster: On my system, touching src/build_test.cc (the slowest
file to build in ninja) and rebuilding ninja_tests is twice as fast than
without this patch. Building all is noticeably faster too: 5.6s with
this patch, 9.1s without this patch (38% faster).

The most noticeable things missing: EXPECT_* and ASSERT_* don't support
streaming notes to them with operator<<, and for failing tests the lhs
and rhs are not printed. That's so that this header does not have to
include sstream, which slows down building ninja_test almost 20%.
If this turns out to be annoying, we can maybe add it.
Add support for --gtest_filter. The bots need it, and it is a useful flag.
Don't support ? and : for --gtest-filter, a bit simpler.

Let me know if you use these!