Fix count_via_win32 on non-win32

When rake does not recognize your platform in CpuCounter it tries all
known methods.  If your platform is not a windows platform you will not
have win32ole so a LoadError was raised but not rescued.

Now the LoadError is rescued so rake can try alternate mechanisms.

See #261

lib/rake/cpu_counter.rb

@@ -51,7 +51,7 @@ def count_via_win32
       wmi = WIN32OLE.connect("winmgmts://")
       cpu = wmi.ExecQuery("select NumberOfCores from Win32_Processor") # TODO count hyper-threaded in this
       cpu.to_enum.first.NumberOfCores
-    rescue StandardError
+    rescue StandardError, LoadError
       nil
     end
 

test/test_rake_cpu_counter.rb

@@ -8,6 +8,14 @@ def setup
     @cpu_counter = Rake::CpuCounter.new
   end
 
+  def test_count_via_win32
+    if Rake::Win32.windows? then
+      assert_kind_of Numeric, @cpu_counter.count_via_win32
+    else
+      assert_nil @cpu_counter.count_via_win32
+    end
+  end
+
   def test_in_path_command
     with_ruby_in_path do |ruby|
       assert_equal ruby, @cpu_counter.in_path_command(ruby)