Fixed memory reporting for Linux systems

/proc/meminfo reports memory in KiloBytes and so needs a multiplier of 1024 instead of 1000.
The kernel reports in terms of pages and the proc filesystem is left shifting by 2 for 4KB pages to get KB. Since this is a binary shift, Bytes will need to shift by 10 and so get multiplied by 1024.

From the kernel code. PAGE_SHIFT = 12 for 4KB pages
"MemTotal:       %8lu kB\n", K(i.totalram)

Closes #131

plugins/system/ps/mem/mem_linux.go

@@ -30,17 +30,17 @@ func VirtualMemory() (*VirtualMemoryStat, error) {
 		}
 		switch key {
 		case "MemTotal":
-			ret.Total = t * 1000
+			ret.Total = t * 1024
 		case "MemFree":
-			ret.Free = t * 1000
+			ret.Free = t * 1024
 		case "Buffers":
-			ret.Buffers = t * 1000
+			ret.Buffers = t * 1024
 		case "Cached":
-			ret.Cached = t * 1000
+			ret.Cached = t * 1024
 		case "Active":
-			ret.Active = t * 1000
+			ret.Active = t * 1024
 		case "Inactive":
-			ret.Inactive = t * 1000
+			ret.Inactive = t * 1024
 		}
 	}
 	ret.Available = ret.Free + ret.Buffers + ret.Cached