Eliminates more warnings during test runs

I've tried to fix everything that I can directly lay my hands on. Some warnings
still stem from the old `.should ==` syntax - that is bound to be replaced.
Others from deep within flexmock - somebody should fix this.

spec/acceptance/examples_spec.rb

@@ -12,7 +12,7 @@ def product_path(str, ext)
       end
 
       it "runs successfully" do
-        stdin, stdout, stderr = Open3.popen3("ruby #{example}")
+        _, stdout, stderr = Open3.popen3("ruby #{example}")
 
         handle_map = {
           stdout => :out, 
@@ -21,7 +21,7 @@ def product_path(str, ext)
         expectation_found = handle_map.any? do |io, ext|
           name = product_path(example, ext)
 
-          if File.exists?(name)
+          if File.exist?(name)
             io.read.strip.should == File.read(name).strip
             true
           end

spec/parslet/atoms_spec.rb

@@ -398,7 +398,7 @@ def call(val)
   end
 
   describe "combinations thereof (regression)" do
-    success=[
+    [
       [(str('a').repeat >> str('b').repeat), 'aaabbb'] 
     ].each do |(parslet, input)|
       describe "#{parslet.inspect} applied to #{input.inspect}" do
@@ -408,7 +408,7 @@ def call(val)
       end 
     end
 
-    inspection=[
+    [
       [str('a'),                              "'a'"                 ], 
       [(str('a') | str('b')).maybe,           "('a' / 'b')?"        ], 
       [(str('a') >> str('b')).maybe,          "('a' 'b')?"          ], 

spec/parslet/transform/context_spec.rb

@@ -27,10 +27,10 @@ def context(*args)
       obj.methods.assert.include?(:a)
     end
     it 'allows inspection' do
-      obj.inspect.assert.match /@a=1/
+      obj.inspect.assert.match(/@a=1/)
     end
     it 'allows conversion to string' do
-      obj.to_s.assert.match /Parslet::Context:0x/
+      obj.to_s.assert.match(/Parslet::Context:0x/)
     end
 
     context 'when the context is enhanced' do

spec/parslet/transform_spec.rb

@@ -6,10 +6,6 @@
   include Parslet
 
   let(:transform) { Parslet::Transform.new }
-  attr_reader :transform
-  before(:each) do
-    @transform = Parslet::Transform.new
-  end
 
   class A < Struct.new(:elt); end
   class B < Struct.new(:elt); end
@@ -157,7 +153,9 @@ class OptimusPrimeJunior < OptimusPrime
       it "should execute in its own context" do
         @bar = 'test'
         transform.call_on_match(bindings, proc do
-          @bar.should_not == 'test'
+          if instance_variable_defined?("@bar")
+            instance_variable_get("@bar").should_not == 'test'
+          end
         end)
       end
     end