Fix getopt_long() usage

The return value of getopt_long() was being stored in a "char".
On some platforms, "char" is unsigned.  In that case, the capstats
command would never work (it would just exit with a usage message).
Fixed by using the correct return value type ("int") of getopt_long().

capstats.cc

@@ -525,9 +525,9 @@ int main(int argc, char **argv)
 {
     while (1) {
 #ifdef USE_DAG
-        char c = getopt_long (argc, argv, "df:i:I:n:Npq:s:lvw:S:", long_options, 0);
+        int c = getopt_long (argc, argv, "df:i:I:n:Npq:s:lvw:S:", long_options, 0);
 #else
-        char c = getopt_long (argc, argv, "f:i:I:n:Npq:s:lvw:S:", long_options, 0);
+        int c = getopt_long (argc, argv, "f:i:I:n:Npq:s:lvw:S:", long_options, 0);
 #endif
 
         if ( c == -1 )