C examples:

- define dummy MPI macros to be used in serial compilation, closing #10
- cleanup some "unused variable" warnings
- fix some format warnings, using C99 format macros

examples/include/examples.h

@@ -0,0 +1,13 @@
+#ifndef __EXAMPLES_H
+#define __EXAMPLES_H
+
+#if !defined (PARALLEL_IO)
+
+#define MPI_COMM_WORLD (0)
+#define MPI_Init(argc, argv)
+#define MPI_Comm_size(comm,nprocs) {comm = 0; *nprocs = 1;}
+#define MPI_Comm_rank(comm,rank)  {comm = 0; (void)(comm); *rank = 0;}
+#define MPI_Finalize()
+
+#endif
+#endif