Include configuration file to headers

Add inclusion to configration file in header files,
instead of relying on other header files to include
the configuration file. This issue resolves #1371
diff --git a/include/mbedtls/ecjpake.h b/include/mbedtls/ecjpake.h
index 59d12f0..010f24a 100644
--- a/include/mbedtls/ecjpake.h
+++ b/include/mbedtls/ecjpake.h
@@ -40,6 +40,11 @@
  * The payloads are serialized in a way suitable for use in TLS, but could
  * also be use outside TLS.
  */
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
 
 #include "ecp.h"
 #include "md.h"