Rescue TypeError when checking for NFS and return false [closes GH-109]

lib/vagrant/hosts/bsd.rb

@@ -7,6 +7,8 @@ module Vagrant
       def nfs?
         system("which nfsd")
         $?.to_i == 0
+      rescue TypeError
+        false
       end
 
       def nfs_export(ip, folders)

test/vagrant/hosts/bsd_test.rb

@@ -26,6 +26,11 @@ class BSDHostTest < Test::Unit::TestCase
 
       assert !@instance.nfs?
     end
+
+    should "not support NFS if an error is raised" do
+      @instance.expects(:system).raises(TypeError.new("foo"))
+      assert !@instance.nfs?
+    end
   end
 
   context "nfs export" do