PUP-1389 Ensure Wide strings has double terminators

It seems that calling String#encode('UTF-16LE') sometimes adds only a single
NULL terminator in both ruby 1.9 and 2.0 on Windows. However, a wide string
is supposed to have two NULL terminators.

For reasons unknown, versions prior to 2012 seem to accept wide strings with
only a single NULL terminator, but in 2012 and 2012R2 the string is often times
contains a non-zero high byte, which causes Windows to read past the single
terminator, and attempt to access a path that does not exist.

Puppet::Util::Windows::File.replace_file now calls FFI to replace files in place 
on Windows. 

In addition, we've removed Windows::API::WideString usages from
everywhere it was found as it is known to cause issues with Windows 2012.
Puppet::Util::Windows::Process.lookup_privilege_value in particular was
changed to use LookupPrivilegeValueA (ANSI) as we control the privilege name
being passed to it.


NOTE: This may have more implications for change once merged to master.