(maint) Fix microsoft_windows feature to return false instead of nil.

Fixing Puppet.features.microsoft_windows? to return false instead of nil.
(maint) Remove unnecessary facter stub in compiler_spec.rb.

Removing an unnecessary facter stub.
The stub is incorrect as value does not return a Fact object.
The correct stub is used below.

Also removing redundant require of puppet/rails.
(PUP-2104) Add cfacter setting to enable cfacter implementation.

Adding a --cfacter setting that will replace the facter implementation
with the native facter implementation if the following conditions are
met:

* cfacter is installed
* the version of cfacter is at least 0.2.0 (not yet released).
* facter has not evaluated any facts by the time the setting is set.

To accomplish this last point, certain default setting values needed to
be delay-evaluated as they relied on facts. Therefore a :default
for a setting now accepts a Proc and calls the Proc only once when the
default value is needed.
Merge pull request #2811 from peterhuene/alternative/facter

(PUP-2104) Add cfacter setting to enable cfacter implementation.