Escape method definition names before using in regexp

I had aliased and monkey patched a [] and was using pry-nav to step through it. When it hit the call() to the aliased parent method, singleton_method_definition choked. 

This pull request wraps the method name inside of Regexp.escape() before using it in the regular expressions. 

    ...earlier in the code...
    alias :parent_square :[] 
    ...later on inside pry...
        53:
        54:   if doit.strip == 'y'
     => 55:     send(:parent_square,args)
        56:   else
        57:     puts "Didn't run it"
        58:   end
        59: end

    [1] pry(#<Sequel::Postgres::Database>)> step

    Frame number: 0/5
    before_session hook failed: RegexpError: empty char-class:   /^define_singleton_method\(?\s*[:\"\'][]|^def\s*self\.[]/
    /usr/local/rvm/gems/ruby-1.9.3-p286@mapfeeder-fulcrum-sync-michael/gems/pry-0.9.12/lib/pry/method.rb:183:in `singleton_method_definition?'
    (see _pry_.hooks.errors to debug)