Merge remote-tracking branch 'rich/platform' into development

* rich/platform:
  Remove dependency on sscanf in lib x509
  Fix extra guard in memory_buffer_alloc
  rebase from development
  implemented macro overriding for polarssl_* library functions
  fix bug introduced by the addition of snprintf and assert macro which caused tests to fail without polarssl_platform_c defined
  add initial symbols to config and checks to check_config to allow use of macros to define standard functions
  reformat and arrange additions to config alphabetically
  add missing checks to check_config
  add macro definition of assert using polarssl_exit
  modify library/memory_buffer_alloc.c, benchmark.c and the tests main code to use polarssl_exit
  add POLARSSL_PLATFORM_EXIT_ALT
  modify scripts/* and tests/* to use polarssl_snprintf
  modify programs/*.c to use polarssl_snprintf
  modify library/debug.c to use polarssl_snprintf
  modify library/x509*.c to use polarssl_snprintf
  modify library/net.c to use polarssl_snprintf
  modify oid.c to use polarssl_snprintf
  add platform_set_snprintf

Conflicts:
	library/memory_buffer_alloc.c
	programs/pkey/pk_sign.c
	programs/pkey/pk_verify.c
	programs/pkey/rsa_sign_pss.c
	programs/pkey/rsa_verify_pss.c
	programs/ssl/ssl_client2.c
	programs/ssl/ssl_pthread_server.c
	programs/test/benchmark.c
	programs/test/ssl_cert_test.c