Extend OS X/Darwin System Calls

[aembke]

It looks like the mach crate currently does not implement the task_info function required to read per-thread CPU and memory information. Until that's updated this module will not be able to handle StatType::Thread on OS X/Darwin. For processes and children POSIX calls seem to work, but for threads Darwin requires using the mach kernel interface.

More info:

• GNU Mach Docs: https://www.gnu.org/software/hurd/gnumach-doc/Task-Information.html
• The Task header file: https://opensource.apple.com/source/xnu/xnu-792.13.8/osfmk/mach/task_info.h.auto.html
• Current implementation: https://github.com/fitzgen/mach/blob/master/src/task.rs
• Examples: http://stackoverflow.com/questions/13893134/get-current-pthread-cpu-usage-mac-os-x, http://stackoverflow.com/questions/5652463/equivalent-to-rusage-thread-darwin

TODO:

• Deal with sizing macros for TASK_BASIC_INFO_COUNT, TASK_EVENTS_INFO_COUNT, and TASK_THREAD_TIMES_INFO_COUNT.
• Implement the new task structs: task_basic_info, task_basic_info_t, task_events_info, task_events_info_t, task_thread_times_info, task_thread_times_info_t, time_value, time_value_t.
• Implement task_info: pub fn task_info(target_task: task_t, flavor: c_int, task_info: *mut task_info_t, task_info_count: *mut mach_msg_type_number_t) -> kern_return_t;