core: add --version option to the ModemManager daemon

It was actually included in the man page of the daemon, but we didn't have it.

src/mm-context.h

@@ -16,8 +16,13 @@
 #ifndef MM_CONTEXT_H
 #define MM_CONTEXT_H
 
+#include <config.h>
 #include <glib.h>
 
+#if !defined(MM_DIST_VERSION)
+# define MM_DIST_VERSION VERSION
+#endif
+
 void mm_context_init (gint argc,
                       gchar **argv);