Add .NET implementation of check_pid

IPython/utils/_process_cli.py

@@ -61,3 +61,13 b' def getoutput(cmd):'
     myError = reg.StandardError
     error = myError.ReadToEnd()
     return output
+
+def check_pid(pid):
+    """
+    Check if a process with the given PID (pid) exists
+    """
+    try:
+        System.Diagnostics.Process.GetProcessById(pid)
+        return True
+    except System.ArgumentException:
+        return False 

IPython/utils/process.py

@@ -23,7 +23,7 b' import sys'
 if sys.platform == 'win32':
     from ._process_win32 import _find_cmd, system, getoutput, arg_split, check_pid
 elif sys.platform == 'cli':
-    from ._process_cli import _find_cmd, system, getoutput, arg_split
+    from ._process_cli import _find_cmd, system, getoutput, arg_split, check_pid
 else:
     from ._process_posix import _find_cmd, system, getoutput, arg_split, check_pid