Fix excess newlines on mosh startup/shutdown.

Fixes #788.

This also works around issues with remote pty typeahead echo corrupting output
from mosh-server.

src/frontend/mosh-client.cc

@@ -192,7 +192,7 @@ int main( int argc, char *argv[] )
     success = false;
   }
 
-  printf( "\n[mosh is exiting.]\n" );
+  printf( "[mosh is exiting.]\n" );
 
   free( key );