tests/test-backwards-remove.t

windows: quote the specified string only when it has to be quoted

Before this patch, "windows.shellquote" (as used as "util.shellquote")
always quotes specified strings with double quotation marks, for
external process invocation.

But some problematic applications can't work correctly, when command
line arguments are quoted: see issue4463 for detail.

On the other hand, quoting itself is needed to specify arguments
containing whitespaces and/or some special characters exactly.

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

  $ hg init
  $ echo This is file a1 > a
  $ hg add a
  $ hg commit -m "commit #0"
  $ ls
  a
  $ echo This is file b1 > b
  $ hg add b
  $ hg commit -m "commit #1"
  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

B should disappear

  $ ls
  a