utop 1.13

1.13 (2014-07-04)
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* don't try to colorize the output when there is too much
* add auto-completion for the `#ppx` directive
* add support for -ppx, -dparsetree and -dsource
* fix compatiblity with OCaml 4.02
* update pa_optcomp
* do not display the camlp4 welcome message