Add macro ENABLE_163_WORKAROUND

I have added this feature into the mailcore2,  the compiler will ignore this feature if someone compile the new version of mailcore2 without this patch and this macro definition.

src/low-level/imap/mailimap.h

@@ -803,6 +803,10 @@ LIBETPAN_EXPORT
 void mailimap_set_logger(mailimap * session, void (* logger)(mailimap * session, int log_type,
     const char * str, size_t size, void * context), void * logger_context);
 
+#ifndef ENABLE_163_WORKAROUND
+  #define ENABLE_163_WORKAROUND
+#endif
+
 LIBETPAN_EXPORT
 int mailimap_is_163_workaround_enabled(mailimap * session);