Try to escape command lines in logfiles

For example, an echo now appears as
  echo "hello world, won't you come out?"
Fixes #815

slave/buildslave/runprocess.py

@@ -31,6 +31,28 @@
 from buildslave import util
 from buildslave.exceptions import AbandonChain
 
+def shell_quote(cmd_list):
+    # attempt to quote cmd_list such that a shell will properly re-interpret
+    # it.  The pipes module is only available on UNIX, and Windows "shell"
+    # quoting is indescribably convoluted - so much so that it's not clear it's
+    # reversible.  Also, the quote function is undocumented (although it looks
+    # like it will be documentd soon: http://bugs.python.org/issue9723).
+    # Finally, it has a nasty bug in some versions where an empty string is not
+    # quoted.
+    #
+    # So:
+    #  - use pipes.quote on UNIX, handling '' as a special case
+    #  - use Python's repr() on Windows, as a best effort
+    if runtime.platformType == 'win32':
+        return " ".join([ `e` for e in cmd_list ])
+    else:
+        import pipes
+        def quote(e):
+            if not e:
+                return '""'
+            return pipes.quote(e)
+        return " ".join([ quote(e) for e in cmd_list ])
+
 class LogFileWatcher:
     POLL_INTERVAL = 2
 
@@ -389,7 +411,8 @@ def _startCommand(self):
                 argv += list(self.command)
             else:
                 argv = self.command
-            display = " ".join(self.fake_command)
+            # Attempt to format this for use by a shell, although the process isn't perfect
+            display = shell_quote(self.fake_command)
 
         # $PWD usually indicates the current directory; spawnProcess may not
         # update this value, though, so we set it explicitly here.  This causes
@@ -399,10 +422,6 @@ def _startCommand(self):
 
         # self.stdin is handled in RunProcessPP.connectionMade
 
-        # first header line is the command in plain text, argv joined with
-        # spaces. You should be able to cut-and-paste this into a shell to
-        # obtain the same results. If there are spaces in the arguments, too
-        # bad.
         log.msg(" " + display)
         self._addToBuffers('header', display+"\n")