win: default shellxescape, shellxquote to empty

Calling cmd.exe in Windows follows a very different pattern from Vim.
The primary difference is that Vim does a nested call to cmd.exe, e.g.
the following call in Vim

    system('echo a 2>&1')

spawns the following processes

    "C:\Program Files (x86)\Vim\vim80\vimrun" -s C:\Windows\system32\cmd.exe /c (echo a 2^>^&1
        ^>C:\Users\dummy\AppData\Local\Temp\VIoC169.tmp 2^>^&1)
    C:\Windows\system32\cmd.exe /c C:\Windows\system32\cmd.exe /c (echo a 2^>^&1
        ^>C:\Users\dummy\AppData\Local\Temp\VIo3C6C.tmp 2^>^&1)
    C:\Windows\system32\cmd.exe  /c (echo a 2>&1
        >C:\Users\dummy\AppData\Local\Temp\VIo3C6C.tmp 2>&1)

The escaping with ^ is needed because cmd.exe calls itself and needs to
preserve the special metacharacters for the last call. However in nvim
no nested call is made, system('') spawns a single cmd.exe process.
Setting shellxescape to "" disables escaping with ^.

The previous default for shellxquote=( wrapped any command in
parenthesis, in Vim this is more meaningful due to the use of tempfiles
to store the output and redirection (also see &shellquote). There is
a slight benefit in having the default be empty because some expressions
that run in console will not run within parens e.g. due to unbalanced
double quotes

    system('echo "a b')

1 files changed, 2 insertions, 12 deletions

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 42d665b42e..9be7dae84d 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -5365,18 +5365,14 @@ A jump table for the options with a short description can be found at |Q_op|.
 	|system()| does not respect this option, it always uses pipes.
 
 						*'shellxescape'* *'sxe'*
-'shellxescape' 'sxe'	string	(default: ""; Windows: "\"&|<>()@^")
+'shellxescape' 'sxe'	string	(default: "")
 			global
 	When 'shellxquote' is set to "(" then the characters listed in this
 	option will be escaped with a '^' character.  This makes it possible
 	to execute most external commands with cmd.exe.
 
 						*'shellxquote'* *'sxq'*
-'shellxquote' 'sxq'	string	(default: "";
-					for Win32, when 'shell' is cmd.exe: "("
-					for Win32, when 'shell' contains "sh"
-					somewhere: "\""
-					for Unix, when using system(): "\"")
+'shellxquote' 'sxq'	string	(default: "")
 			global
 	Quoting character(s), put around the command passed to the shell, for
 	the "!" and ":!" commands.  Includes the redirection.  See
@@ -5385,12 +5381,6 @@ A jump table for the options with a short description can be found at |Q_op|.
 	When the value is '(' then ')' is appended. When the value is '"('
 	then ')"' is appended.
 	When the value is '(' then also see 'shellxescape'.
-	This is an empty string by default on most systems, but is known to be
-	useful for on Win32 version, either for cmd.exe which automatically
-	strips off the first and last quote on a command, or 3rd-party shells
-	such as the MKS Korn Shell or bash, where it should be "\"".  The
-	default is adjusted according the value of 'shell', to reduce the need
-	to set this option by the user.
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.