use printf instead of echo

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/echo.html#tag_20_37_16

CHANGELOG.md

@@ -3,6 +3,8 @@
   - Proper error handling for not enough arguments to `box` commands.
   - Fix issue causing crashes with bridged networking. [GH-673]
   - Ignore host only network interfaces that are "down." [GH-675]
+  - Use "printf" instead of "echo" to determine shell expanded files paths
+    which is more generally POSIX compliant. [GH-676]
 
 ## 0.9.2 (January 20, 2012)
 

lib/vagrant/guest/linux.rb

@@ -47,7 +47,7 @@ module Vagrant
         # else, things like '~' don't expand properly in shared folders. We have
         # to `echo` here to get that path.
         real_guestpath = nil
-        @vm.channel.execute("echo #{guestpath}") do |type, data|
+        @vm.channel.execute("printf #{guestpath}") do |type, data|
           if type == :stdout
             real_guestpath ||= ""
             real_guestpath += data