adding handlers for dimacs for solver_from_file, and opb, wncf for opt_from_file, #1361

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/util/file_path.h

@@ -0,0 +1,38 @@
+/*++
+Copyright (c) 2017 Microsoft Corporation
+
+Module Name:
+
+    file_path.h
+
+Abstract:
+
+    File path functions.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2017-11-19
+
+Revision History:
+
+--*/
+#ifndef FILE_PATH_H_
+#define FILE_PATH_H_
+
+inline char const * get_extension(char const * file_name) {
+    if (file_name == 0)
+        return 0;
+    char const * last_dot = 0;
+    for (;;) {
+        char const * tmp = strchr(file_name, '.');
+        if (tmp == 0) {
+            return last_dot;
+        }
+        last_dot  = tmp + 1;
+        file_name = last_dot;
+    }
+}
+
+#endif /* FILE_PATH_H_ */
+
+