Modified Cron to add AIX Crontab support, changed according to suggestions

from mpdehaan and redone entirely.

system/cron

@@ -352,6 +352,8 @@ class CronTab(object):
         if self.user:
             if platform.system() == 'SunOS':
                 return "su %s -c '%s -l'" % (pipes.quote(self.user), pipes.quote(CRONCMD))
+            elif platform.system() == 'AIX':
+                return "%s -l %s" % (pipes.quote(CRONCMD), (pipes.quote(self.user))
             else:
                 user = '-u %s' % pipes.quote(self.user)
         return "%s %s %s" % (CRONCMD , user, '-l')
@@ -362,7 +364,7 @@ class CronTab(object):
         """
         user = ''
         if self.user:
-            if platform.system() == 'SunOS':
+            if platform.system() in [ 'SunOS', 'AIX' ]:
                 return "chown %s %s ; su '%s' -c '%s %s'" % (pipes.quote(self.user), pipes.quote(path), pipes.quote(self.user), CRONCMD, pipes.quote(path))
             else:
                 user = '-u %s' % pipes.quote(self.user)