PP trick for long inspect code

[ko1]

• Stop pp when the output exceeds the maximum length
• Use PP.singleline_pp to disable breaking features

fix #635

This does not solve the problem if the pretty_print consumes
time for example using network connections.

[ko1]

class C
  def initialize
    @a = ['x'] * 10_000
    @b = ['y'] * 10_000
    @c = ['z'] * 10_000
  end
end

$obj = C.new

def rec0 o = $obj
  a = 0
  binding.b
end


(1..1000).each{|i|
  eval("def rec#{i}(o = $obj) = (a = #{i}; rec#{i-1})\n")
}

rec1000

$ time exe/rdbg  -n target.rb -e 'bt;;c

# before
real    0m7.428s
user    0m7.055s
sys     0m0.154s

# after
real    0m0.799s
user    0m0.504s
sys     0m0.111s