Revert "Use Popen to start processes (joh#46)"

This commit introduced a bug where the command would only run once if
multiple files are changed at the same time. This revert closes joh#49.

This reverts commit ea2cf37.

whenchanged/whenchanged.py

@@ -59,7 +59,6 @@ def __init__(self, files, command, recursive=False, run_once=False, run_at_start
         self.last_run = 0
 
         self.observer = Observer(timeout=0.1)
-        self.process = None
 
         for p in self.paths:
             if os.path.isdir(p):
@@ -75,27 +74,12 @@ def run_command(self, thefile):
         if self.run_once:
             if os.path.exists(thefile) and os.path.getmtime(thefile) < self.last_run:
                 return
-
-        if self.is_running_process():
-            self.stop_current_process()
-
         new_command = []
         for item in self.command:
             new_command.append(item.replace('%f', thefile))
-
-        self.start_process(new_command)
-
-    def start_process(self, command):
-        is_shell_command = len(command) == 1
-        self.process = subprocess.Popen(command, shell=is_shell_command)
+        subprocess.call(new_command, shell=(len(new_command) == 1))
         self.last_run = time.time()
 
-    def stop_current_process(self):
-        self.process.kill()
-
-    def is_running_process(self):
-        return bool(self.process) and self.process.poll() is None
-
     def is_interested(self, path):
         if self.exclude.match(path):
             return False