Don't raise for unrecognized options.

When calling Pry.new() or Pry#refresh and passing custom options these options
should not be set (and therefor prevent NoMethodErrors from popping up).

Signed-off-by: Yorick Peterse <yorickpeterse@gmail.com>

lib/pry/pry_instance.rb

@@ -59,7 +59,7 @@ class Pry
     end
 
     defaults.merge!(options).each do |key, value|
-      send "#{key}=", value
+      send("#{key}=", value) if respond_to?("#{key}=")
     end
 
     true

test/test_pry.rb

@@ -1322,4 +1322,12 @@ describe Pry do
         end
       end
     end
+
+    describe 'setting custom options' do
+      it 'should not raise for unrecognized options' do
+        should.not.raise?(NoMethodError) {
+          instance = Pry.new(:custom_option => 'custom value')
+        }
+      end
+    end
   end