Windows: improve indexing process management. Fix Pidfile locking.

Use a stop file to request stop of indexing when the indexer was not
started from the current GUI instance.

src/common/rclconfig.cpp

@@ -1377,6 +1377,10 @@ string RclConfig::getPidfile() const
 {
     return path_cat(getCacheDir(), "index.pid");
 }
+string RclConfig::getIdxStopFile() const
+{
+    return path_cat(getCacheDir(), "index.stop");
+}
 
 /* Eliminate the common leaf part of file paths p1 and p2. Example: 
  * /mnt1/common/part /mnt2/common/part -> /mnt1 /mnt2. This is used

src/common/rclconfig.h

@@ -203,6 +203,7 @@ class RclConfig {
     string getPidfile() const;
     /** Get indexing status file name */
     string getIdxStatusFile() const;
+    string getIdxStopFile() const;
     /** Do path translation according to the ptrans table */
     void urlrewrite(const string& dbdir, string& url) const;
     ConfSimple *getPTrans() {