tests/test-cat.t

posix: quote the specified string only when it may have to be quoted

This patch makes "posix.shellquote" examine the specified string and
quote it only when it may have to be quoted for safety, like as the
previous patch for "windows.shellquote".

In fact, on POSIX environment, quoting itself doesn't cause issues
like issue4463. But (almost) equivalent quoting policy can avoid
examining test result differently on POSIX and Windows (even though
showing command line with "%r" causes such examination in
"test-extdiff.t").

The last hunk for "test-extdiff.t" in this patch isn't needed for the
previous patch for "windows.shellquote", because the code path of it
is executed only "#if execbit" (= avoided on Windows).

  $ hg init
  $ echo 0 > a
  $ echo 0 > b
  $ hg ci -A -m m
  adding a
  adding b
  $ hg rm a
  $ hg cat a
  0
  $ hg cat --decode a # more tests in test-encode
  0
  $ echo 1 > b
  $ hg ci -m m
  $ echo 2 > b
  $ hg cat -r 0 a
  0
  $ hg cat -r 0 b
  0
  $ hg cat -r 1 a
  a: no such file in rev 7040230c159c
  [1]
  $ hg cat -r 1 b
  1

Test fileset

  $ echo 3 > c
  $ hg ci -Am addmore c
  $ hg cat 'set:not(b) or a'
  3
  $ hg cat 'set:c or b'
  1
  3

  $ mkdir tmp
  $ hg cat --output tmp/HH_%H c
  $ hg cat --output tmp/RR_%R c
  $ hg cat --output tmp/h_%h c
  $ hg cat --output tmp/r_%r c
  $ hg cat --output tmp/%s_s c
  $ hg cat --output tmp/%d%%_d c
  $ hg cat --output tmp/%p_p c
  $ hg log -r . --template "{rev}: {node|short}\n"
  2: 45116003780e
  $ find tmp -type f | sort
  tmp/.%_d
  tmp/HH_45116003780e3678b333fb2c99fa7d559c8457e9
  tmp/RR_2
  tmp/c_p
  tmp/c_s
  tmp/h_45116003780e
  tmp/r_2