10.2 integration fixes

- changed plugin API to avoid crashes: Oracle/MariaDB changed
    structure several times without updating interface version.
  - ABI fixes: moved additional net items to net->extension (connection
    handler and com_multi buffer)

libmariadb/ma_string.c

@@ -124,4 +124,11 @@ void ma_dynstr_free(DYNAMIC_STRING *str)
   }
 }
 
-
+char *ma_strmake(register char *dst, register const char *src, size_t length)
+{
+  while (length--)
+    if (! (*dst++ = *src++))
+      return dst-1;
+  *dst=0;
+  return dst;
+}