bug#25315: diffoscope misses inputs

[Ricardo Wurmus]

I just installed diffoscope and ran it on two files and got this error:

--8<---------------cut here---------------start------------->8---
diffoscope 
/gnu/store/lf2ybanhxpvbgbxcsxmc733v010g15fp-clisp-2.49/lib/clisp-2.49/base/lispinit.mem
 
/gnu/store/lf2ybanhxpvbgbxcsxmc733v010g15fp-clisp-2.49-check/lib/clisp-2.49/base/lispinit.mem
--- 
/gnu/store/lf2ybanhxpvbgbxcsxmc733v010g15fp-clisp-2.49/lib/clisp-2.49/base/lispinit.mem
+++ 
/gnu/store/lf2ybanhxpvbgbxcsxmc733v010g15fp-clisp-2.49-check/lib/clisp-2.49/base/lispinit.mem
│┄ xxd not available in path. Falling back to Python hexlify.

Traceback (most recent call last):
  File 
"/gnu/store/i0rn71jcspqr6p9lbfrghh2xkv5gmp77-diffoscope-63/lib/python3.5/site-packages/diffoscope/main.py",
 line 290, in main
    sys.exit(run_diffoscope(parsed_args))
  File 
"/gnu/store/i0rn71jcspqr6p9lbfrghh2xkv5gmp77-diffoscope-63/lib/python3.5/site-packages/diffoscope/main.py",
 line 268, in run_diffoscope
    output_text(difference, print_func=print_func, color=color)
  File 
"/gnu/store/i0rn71jcspqr6p9lbfrghh2xkv5gmp77-diffoscope-63/lib/python3.5/site-packages/diffoscope/presenters/text.py",
 line 59, in output_text
    print_difference(difference, print_func, color)
  File 
"/gnu/store/i0rn71jcspqr6p9lbfrghh2xkv5gmp77-diffoscope-63/lib/python3.5/site-packages/diffoscope/presenters/text.py",
 line 34, in print_difference
    diff_output = color_unified_diff(difference.unified_diff)
  File 
"/gnu/store/i0rn71jcspqr6p9lbfrghh2xkv5gmp77-diffoscope-63/lib/python3.5/site-packages/diffoscope/__init__.py",
 line 69, in tool_check
    raise RequiredToolNotFound(command)
diffoscope.exc.RequiredToolNotFound: colordiff
--8<---------------cut here---------------end--------------->8---

We either need to add xxd (from vim) or colordiff.

-- 
Ricardo

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