server: workaround for idiotic ArchLinux renaming of python to python2.

First try running under python2, then python if that doesn't exist.

main.py

@@ -54,7 +54,7 @@ l,listen=  transproxy to this ip address and port number [127.0.0.1:0]
 H,auto-hosts scan for remote hostnames and update local /etc/hosts
 N,auto-nets  automatically determine subnets to route
 dns        capture local DNS requests and forward to the remote DNS server
-python=    path to python interpreter on the remote server [python]
+python=    path to python interpreter on the remote server
 r,remote=  ssh hostname (and optional username) of remote sshuttle server
 x,exclude= exclude this subnet (can be used more than once)
 v,verbose  increase debug message verbosity

ssh.py

@@ -73,16 +73,23 @@ def connect(ssh_cmd, rhostport, python, stderr, options):
 
         
     if not rhost:
-        argv = [python, '-c', pyscript]
+        # ignore the --python argument when running locally; we already know
+        # which python version works.
+        argv = [sys.argv[1], '-c', pyscript]
     else:
         if ssh_cmd:
             sshl = ssh_cmd.split(' ')
         else:
             sshl = ['ssh']
+        if python:
+            pycmd = "'%s' -c '%s'" % (python, pyscript)
+        else:
+            pycmd = ("P=python2; $P -V 2>/dev/null || P=python; "
+                     "\"$P\" -c '%s'") % pyscript
         argv = (sshl + 
                 portl + 
                 ipv6flag + 
-                [rhost, '--', "'%s' -c '%s'" % (python, pyscript)])
+                [rhost, '--', pycmd])
     (s1,s2) = socket.socketpair()
     def setup():
         # runs in the child process