Don't duplicate names when defining new machines in VFile

CHANGELOG.md

@@ -77,6 +77,8 @@ BUG FIXES:
   - `config.ssh` settings override all detected SSH settings (regression). [GH-1479]
   - `ssh-config` won't raise an exception if the VirtualBox machine
     is not created. [GH-1562]
+  - Multiple machines defined in the same Vagrantfile with the same
+    name will properly merge.
 
 ## 1.1.6 (April 3, 2013)
 

plugins/kernel_v2/config/vm.rb

@@ -172,7 +172,7 @@ module VagrantPlugins
 
         # Add the name to the array of VM keys. This array is used to
         # preserve the order in which VMs are defined.
-        @__defined_vm_keys << name
+        @__defined_vm_keys << name if !@__defined_vm_keys.include?(name)
 
         # Add the SubVM to the hash of defined VMs
         if !@__defined_vms[name]