Replace IO::Pty with pipe

Now when we don't need some fancy pty for sending on window-size and
reading proxy-output from, just use a regular pipe to drop dependency on
IO::Pty

[closes #378]

scripts/mosh

@@ -195,12 +195,6 @@ if ( scalar @ARGV < 1 ) {
 my $userhost = shift;
 my @command = @ARGV;
 
-# Run SSH and read password
-my $pty = new IO::Pty;
-my $pty_slave = $pty->slave;
-
-$pty_slave->clone_winsize_from( \*STDIN );
-
 # Count colors
 open COLORCOUNT, '-|', $client, ('-c') or die "Can't count colors: $!\n";
 my $colors = "";
@@ -218,14 +212,15 @@ if ( (not defined $colors)
   $colors = 0;
 }
 
+my ($p_read, $p_write);
+pipe($p_read, $p_write);
 my $pid = fork;
 die "$0: fork: $!\n" unless ( defined $pid );
 if ( $pid == 0 ) { # child
-  $pty->close_slave();
-  open STDOUT, ">&", $pty or die;
-  open STDERR, ">&", $pty or die;
-  open STDIN, "<&", $pty or die;
-  close $pty;
+  open STDOUT, ">&", $p_write or die;
+  open STDERR, ">&", $p_write or die;
+  close $p_write;
+  close $p_read;
 
   my @server = ( 'new', '-s' );
 
@@ -249,8 +244,8 @@ if ( $pid == 0 ) { # child
 } else { # parent
   my ( $ip, $port, $key );
   my $bad_udp_port_warning = 0;
-  close $pty;
-  LINE: while ( <$pty_slave> ) {
+  close $p_write;
+  LINE: while ( <$p_read> ) {
     chomp;
     if ( m{^MOSH IP } ) {
       if ( defined $ip ) {
@@ -271,7 +266,7 @@ if ( $pid == 0 ) { # child
     }
   }
   waitpid $pid, 0;
-  close $pty_slave;
+  close $p_read;
 
   if ( not defined $ip ) {
       die "$0: Did not find remote IP address (is SSH ProxyCommand disabled?).\n";