Fix missing public include directory

Fix double-free in unit test on Windows.

Link libpthread when necessary in CMake builds

Path "<prefix>/include" will not be added to the headers search of dependent
targets without specifying INSTALL_INTERFACE, i.e. compilation
will fail with error:

  "fatal error: 'glog/logging.h' file not found".

The LOG_SYSRESULT refers to result twice.  Since, in this test,
result expands to FindClose(handle), the handle was being freed twice.

Fixed warning caused by policy CMP0063 introduced in CMake 3.3

Allow to disable multithreading support using CMake

[#23] Add logfile_mode to control logfile permissions

This commit additionally enables threading for win32 by default.

Fix mocklog unused arguments

Fix redefinition of _XOPEN_SOURCE.

Don't call RAW_VLOG with locking vmodule_lock

SetVLOGLevel locks vmodule_lock however RAW_VLOG at the end also implicitly locks it via InitVLOG3__.
This causes deadlock/segfault.

fixes #29 

delete LogDestination::sinks_ at DeleteLogDestinations(). 

fixes #8 

Add CMake support. closes #4 

Under Debian Jessie, I get a warning about redefining _XOPEN_SOURCE
which is easy to fix.

SetVLOGLevel locks vmodule_lock however RAW_VLOG at the end also implicitly locks it via InitVLOG3__.

This causes deadlock/segfault.

Guard GOOGLE_PREDICT_TRUE|FALS with #ifndef to avoid collision with other google opensource projects like protobuf.