fixed qemu path and added some kind of autodetection as multiple platform...

fixed qemu path and added some kind of autodetection as multiple platform emulators are available on ubuntu 14.04

src/utils/pintos

@@ -619,7 +619,19 @@ sub run_qemu {
       if $vga eq 'terminal';
     print "warning: qemu doesn't support jitter\n"
       if defined $jitter;
-    my (@cmd) = ('qemu');
+
+    # on newer systems (e.g. Ubuntu 14.04) there are
+    # various versions of qemu for different platforms available.
+    # if there are multiple versions, we should select the
+    # complete system emulator for i386 platforms.
+    my ($qemu) = find_in_path ("qemu");
+    if (!defined $qemu) {
+        $qemu = find_in_path("qemu-system-i386");
+        die "unable to autodetect qemu. please check if it is installed\n"
+          if !defined $qemu;
+    }
+
+    my (@cmd) = ($qemu);
     push (@cmd, '-hda', $disks[0]) if defined $disks[0];
     push (@cmd, '-hdb', $disks[1]) if defined $disks[1];
     push (@cmd, '-hdc', $disks[2]) if defined $disks[2];