Run batch file with cmd.exe. Quoted user command.

It seems that we have to specify the full path to cmd.exe in the first
argument of CreateProcess() to run batch file in proper manner.  We
first determine the full path to cmd.exe. To do this, we get windir
environment variable and concatenate it with "\system32\cmd.exe".

src/util.cc

@@ -1478,12 +1478,12 @@ void executeHook
 {
   const std::string gidStr = util::itos(gid);
   const std::string numFilesStr = util::uitos(numFiles);
+#ifndef __MINGW32__
   A2_LOG_INFO(fmt("Executing user command: %s %s %s %s",
                   command.c_str(),
                   gidStr.c_str(),
                   numFilesStr.c_str(),
                   firstFilename.c_str()));
-#ifndef __MINGW32__
   pid_t cpid = fork();
   if(cpid == -1) {
     A2_LOG_ERROR("fork() failed. Cannot execute user command.");
@@ -1506,11 +1506,30 @@ void executeHook
 
   memset(&pi, 0, sizeof (pi));
 
-  std::string cmdline = command;
+  bool batch = util::endsWith(util::toLower(command), ".bat");
+  std::string cmdline;
+  std::string cmdexe;
+  if(batch) {
+    const char* p = getenv("windir");
+    if(p) {
+      cmdexe = std::string(p);
+      cmdexe += "\\system32\\cmd.exe";
+    } else {
+      A2_LOG_INFO("Failed to get windir environment variable."
+                  " Executing batch file will fail.");
+      // TODO Might be useless.
+      cmdexe = "cmd.exe";
+    }
+    cmdline += "/C \"";
+  }
+  strappend(cmdline, "\"", command, "\"");
   strappend(cmdline, " ", gidStr, " ", numFilesStr, " \"", firstFilename, "\"");
-
+  if(batch) {
+    cmdline += "\"";
+  }
+  A2_LOG_INFO(fmt("Executing user command: %s", cmdline.c_str()));
   DWORD rc = CreateProcess(
-                           NULL,
+                           batch ? cmdexe.c_str() : NULL,
                            (LPSTR)cmdline.c_str(),
                            NULL,
                            NULL,