tests/test-fuzz-targets.t

debugcommands: print out the editor that was searched for (post shlexsplit)

A user was in #mercurial and had the following settings in their hgrc:

  [ui]
  editor = C:\home\npp\notepad++.exe -multiInst -nosession

After shlexsplit, the first argument was mangled into C:homenppnotepad++.exe,
which was quite unlikely to exist.  It took many back-and-forths to identify
that adding " characters around the exe would fix the issue; we were thinking
that it's because something was incorrectly *not* splitting and adding/moving
the " characters fixed the split boundaries, but when testing afterward it
appears that it's just mangled.

I considered adding an informational if pycompat.iswindows and \ in the string
about this issue, but was worried that might have too many false positives and
did not do so at this time.

Differential Revision: https://phab.mercurial-scm.org/D1808

#require clang-libfuzzer test-repo
  $ cd $TESTDIR/../contrib/fuzz
  $ make
Just run the fuzzer for five seconds to verify it works at all.
  $ ./bdiff -max_total_time 5