Merge branch 'mbedtls-1.3' into development

* mbedtls-1.3:
  Include changes from the 1.2 branch
  Remove unused headers in o_p_test
  Add countermeasure against cache-based lucky 13
  Make results of (ext)KeyUsage accessible
  Fix missing NULL check in MPI
  Fix detection of getrandom()
  Fix "make install" handling of symlinks
  Fix bugs in programs displaying verify flags

Conflicts:
	Makefile
	include/polarssl/ssl.h
	library/entropy_poll.c
	library/ssl_srv.c
	library/ssl_tls.c
	programs/test/o_p_test.c
	programs/test/ssl_cert_test.c
	programs/x509/cert_app.c

include/mbedtls/bignum.h

@@ -150,7 +150,9 @@ typedef struct
 mbedtls_mpi;
 
 /**
- * \brief           Initialize one MPI
+ * \brief           Initialize one MPI (make internal references valid)
+ *                  This just makes it ready to be set or freed,
+ *                  but does not define a value for the MPI.
  *
  * \param X         One MPI to initialize.
  */