Don't rely on Thread constant [Fixes #629]

lib/pry/default_commands/context.rb

@@ -42,7 +42,7 @@ class Pry
           if opts.quiet? && (internal_binding? || !code?)
             return
           elsif internal_binding?
-            output.puts "Could not find local context, did you use \`binding.pry\`?"
+            output.puts "Insert #{target_self.inspect}"
             return
           end
 

lib/pry/pry_instance.rb

@@ -144,7 +144,7 @@ class Pry
   # @return [Object] The value the local was set to.
   def inject_local(name, value, b)
     Thread.current[:__pry_local__] = value.is_a?(Proc) ? value.call : value
-    b.eval("#{name} = Thread.current[:__pry_local__]")
+    b.eval("#{name} = ::Thread.current[:__pry_local__]")
   ensure
     Thread.current[:__pry_local__] = nil
   end