Explicitly disable dumping core (closes #72)

This is a precaution to avoid saving sensitive data to disk, e.g. session keys.
We expect that corefiles are not world readable, but they're still sitting on
the physical disk and it's safer just to disable creating them.

GitHub issue #71 deals with a similar concern.

src/frontend/mosh-client.cc

@@ -54,6 +54,9 @@ void print_colorcount( void )
 
 int main( int argc, char *argv[] )
 {
+  /* For security, make sure we don't dump core */
+  Crypto::disable_dumping_core();
+
   /* Get arguments */
   int opt;
   while ( (opt = getopt( argc, argv, "c" )) != -1 ) {

src/frontend/mosh-server.cc

@@ -103,6 +103,9 @@ string get_SSH_IP( void )
 
 int main( int argc, char *argv[] )
 {
+  /* For security, make sure we don't dump core */
+  Crypto::disable_dumping_core();
+
   char *desired_ip = NULL;
   char *desired_port = NULL;
   char **command = NULL;