Process.PagedMemorySize64 now returns value from /proc/PID/status

Kernels after 2.12 report VmSwap status in /proc (see https://www.kernel.org/doc/Documentation/filesystems/proc.txt). Mono exposes some memory info via System.Diagnostics.Process but not swap/paging info. Knowing page/swap state is critcal for my app since it maintains large in-memory caches.

Simple test code:
```
using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

public static class Program
{
	public static void Main(string[] args)
	{
		var process = System.Diagnostics.Process.GetCurrentProcess();
		
		long physicalMemorySize = -1;
		var pc = new PerformanceCounter("Mono Memory", "Total Physical Memory"); 
		if (pc.RawValue > 0)
		{
			physicalMemorySize = pc.RawValue;
		}
				
		int blocks = (int)(physicalMemorySize / 1024);
		int blockSize = blocks;
		var emptyData = new byte[blockSize];
		for (int i = 0; i < 1024; i++)
		{			
			var data = Marshal.AllocHGlobal(blockSize);
			Marshal.Copy(emptyData, 0, data, blockSize);			
		}
		
		var msg = string.Format(			
			"Process: id={0}\n" +
			"CPU: user={1:N1}s, total={2:N1}s\n" +
			"Threads: count={3}\n" +
			"Memory: physical={4:N}MB, working={5:N0}MB, virtual={6:N0}MB, private={7:N0}MB, paged={8:N0}MB\n" +
			"GC: totalMemory={9:N0}MB, count0={10}, count1={11}",
			process.Id, 
			process.UserProcessorTime.TotalSeconds, process.TotalProcessorTime.TotalSeconds,
			process.Threads.Count,
			physicalMemorySize >> 20, process.WorkingSet64 >> 20, process.VirtualMemorySize64 >> 20, process.PrivateMemorySize64 >> 20, process.PagedMemorySize64 >> 20,                    
			GC.GetTotalMemory(false) >> 20, GC.CollectionCount(0), GC.CollectionCount(1));		
			
		Console.WriteLine(msg);
		
		Console.ReadLine();
	}
}
```
If the entry is missing from /proc/PIB/status we will end up with 0 just like before