S/MIME mail parser not used, but compiled

Due to missing config.h the ENABLE_SMIME was not declared, thus the type
for the S/MIME parser was not registered, neither used, which showed
S/MIME signed or encrypted messages as attachments, instead of deciphering
their content.

em-format/e-mail-parser.c

@@ -15,6 +15,10 @@
  *
  */
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include "e-mail-parser.h"
 
 #include <string.h>