Remove the "lone pipe" exception in ShellCommand argument handling

As discussed in
<http://news.gmane.org/find-root.php?group=gmane.comp.python.buildbot.devel&article=10518>.
This makes it possible to pass a pipe as an argument, plus it makes argument
handling consistent between Windows and Unix-likes.

master/docs/manual/cfg-buildsteps.rst

@@ -1002,9 +1002,6 @@ The :bb:step:`ShellCommand` arguments are:
 
     If ``command`` contains nested lists (for example, from a properties substitution), then that list will be flattened before it is executed.
 
-    On the topic of shell metacharacters, note that in DOS the pipe character (``|``) is conditionally escaped (to ``^|``) when it occurs inside a more complex string in a list of strings.
-    It remains unescaped when it occurs as part of a single string or as a lone pipe in a list of strings.
-
 ``workdir``
     All ShellCommands are run by default in the ``workdir``, which defaults to the :file:`build` subdirectory of the slave builder's base directory.
     The absolute path of the workdir will thus be the slave's basedir (set as an option to ``buildslave create-slave``, :ref:`Creating-a-buildslave`) plus the builder's basedir (set in the builder's ``builddir`` key in :file:`master.cfg`) plus the workdir itself (a class-level attribute of the BuildFactory, defaults to :file:`build`).

master/docs/relnotes/index.rst

@@ -295,6 +295,12 @@ Deprecations, Removals, and Non-Compatible Changes
   Buildbot-slave-0.9.0 will still run successfully against Buildbot-0.8.9 or earlier, configured to use old-style steps.
   However, the support is stlil deprecated and will be removed as soon as it is inconvenient for developers.
 
+* On Windows, if a :bb:step:`ShellCommand` step in which ``command`` was specified as a list is executed, and a
+  list element is a string consisting of a single pipe character, it no longer creates a pipeline.
+  Instead, the pipe character is passed verbatim as an argument to the program, like any other string.
+  This makes command handling consistent between Windows and Unix-like systems.
+  To have a pipeline, specify ``command`` as a string.
+
 Details
 -------
 

slave/buildslave/runprocess.py

@@ -49,12 +49,7 @@ def win32_batch_quote(cmd_list):
     # Quote cmd_list to a string that is suitable for inclusion in a
     # Windows batch file. This is not quite the same as quoting it for the
     # shell, as cmd.exe doesn't support the %% escape in interactive mode.
-    # As an exception, a lone pipe as an argument is not escaped, and
-    # becomes a shell pipe.
     def escape_arg(arg):
-        if arg == '|':
-            return arg
-
         arg = quoteArguments([arg])
         # escape shell special characters
         arg = re.sub(r'[@()^"<>&|]', r'^\g<0>', arg)

slave/buildslave/test/unit/test_runprocess.py

@@ -282,23 +282,6 @@ def check(ign):
         d.addCallback(check)
         return d
 
-    @compat.skipUnlessPlatformIs("win32")
-    def testPipeAlone(self):
-        b = FakeSlaveBuilder(False, self.basedir)
-        # this is highly contrived, but it proves the point.
-        cmd = stdoutCommand("b\\na")
-        cmd[0] = cmd[0].replace(".exe", "")
-        cmd.extend(['|', 'sort'])
-        s = runprocess.RunProcess(b, cmd, self.basedir)
-
-        d = s.start()
-
-        def check(ign):
-            self.failUnless({'stdout': nl('a\nb\n')} in b.updates, b.show())
-            self.failUnless({'rc': 0} in b.updates, b.show())
-        d.addCallback(check)
-        return d
-
     @compat.skipUnlessPlatformIs("win32")
     def testPipeString(self):
         b = FakeSlaveBuilder(False, self.basedir)