add coverity model file

This defines behaviour of functions that Coverity Scan is not aware of.
The file has no immediate effect. A user with the Maintainer/Owner role on scan.coverity.com has to upload the file in order to make it work.

coverity-model.cpp

@@ -0,0 +1,42 @@
+// This file is part of BOINC.
+// http://boinc.berkeley.edu
+// Copyright (C) 2015 University of California
+//
+// BOINC is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation,
+// either version 3 of the License, or (at your option) any later version.
+//
+// BOINC is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with BOINC.  If not, see <http://www.gnu.org/licenses/>.
+
+/*
+ * Coverity Scan Modeling file for BOINC
+ * 
+ * This defines behaviour of functions that Coverity Scan is not aware of.
+ * 
+ * For how to create a model see: 
+ * https://scan.coverity.com/tune and https://scan.coverity.com/models#overriding
+ * 
+ * If you add anything here it has no immediate effect. A user with the 
+ * Maintainer/Owner role on scan.coverity.com has to upload the file to 
+ * https://scan.coverity.com/projects/boinc-boinc?tab=analysis_settings
+ * 
+ **/
+
+// the dir string is kind of sanitized here
+// prevents tainted string defects involving SCHED_CONFIG::project_path()
+//
+bool is_project_dir(const char *dir) {
+    bool ok_string;
+    if (ok_string == true) {
+        __coverity_tainted_string_sanitize_content__((void*)dir);
+        return true;
+    }
+    return false;
+}