Base the default SSL ciphers on DEFAULT instead of ALL

It's better to start from what the OpenSSL people consider a good
default and then remove insecure things (low encryption, exportable
encryption and md5 at this point) from that, instead of starting
from everything that exists and remove from that. We trust the
OpenSSL people to make good choices about what the default is.

src/backend/utils/misc/guc.c

@@ -3056,7 +3056,7 @@ static struct config_string ConfigureNamesString[] =
 		},
 		&SSLCipherSuites,
 #ifdef USE_SSL
-		"ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH",
+		"DEFAULT:!LOW:!EXP:!MD5:@STRENGTH",
 #else
 		"none",
 #endif

src/backend/utils/misc/postgresql.conf.sample

@@ -79,7 +79,7 @@
 
 #authentication_timeout = 1min		# 1s-600s
 #ssl = off				# (change requires restart)
-#ssl_ciphers = 'ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH'	# allowed SSL ciphers
+#ssl_ciphers = 'DEFAULT:!LOW:!EXP:!MD5:@STRENGTH'	# allowed SSL ciphers
 					# (change requires restart)
 #ssl_renegotiation_limit = 512MB	# amount of data between renegotiations
 #ssl_cert_file = 'server.crt'		# (change requires restart)