Add Lei Xu to AUTHORS and CONTRIBUTORS

fix examples to use SetBytesProcessed

- use State::SetBytesProcessed not SetBenchmarkBytesProcessed

fix building on ubuntu

Fix a bug in the destruction of BenchmarkFamilies.

Take the CPU time into account in PauseTiming/ResumeTiming

Conflicts:
	src/benchmark.cc

Fix the stddev/mean computations

Two bug fixes in KeepRunning

Conflicts:
	src/benchmark.cc

Fix the stddev/mean computations which had be garbled since commit e5f5a0d3, leading to a mean that was not in the min/max range and to zero-divide in the stddev computation, among others.

Resolve race on approx_time_ in FastClock.

Statically initialize benchmark_mutex and extend its lifetime.

Resolve benchmark cleanup race condition in issue #20.

InitType should hold a lock before storing to approx_time_, which is later
read by the background worker.  When the worker is actively running (i.e., not
blocked on bg_cond_) it holds bg_mutex_.

InitType is called during benchmark setup only, so any contention induced for
the mutex should not have performance/accuracy consequences.

RunSpecifiedBenchmarks destroys benchmark_mutex before its last usage,
typically in RemoveBenchmark during cleanup of the BenchmarkFamilies singleton.

The multithreaded API for benchmarks provides that teardown can happen in
thread 0.  For this to be safe, all other threads executing the benchmark
function need to have exited.  Otherwise, thread 0 may begin to teardown shared
resources before the other threads have stopped using these resources as they
are in their last loop of while (KeepRunning()) { ... }.

This change creates a single exit point for KeepRunning() to return false.
When running a multithreaded benchmark, thread 0 blocks on KeepRunning() until
all other threads have exited.  This approach allows for there to be no change
to the user-facing API exemplified in the BM_MultiThreaded example.

Remove URL_HASH and TLS_VERIFY from CMake configuration.

Per the CMake 2.8.0 documentation, these options did not exist for
ExternalProject_Add.  These options were added in CMake 2.8.10.