Change the built-in default socket directory to be /run/postgresql.
This is to resolve communication problems with clients operating
under systemd's PrivateTmp environment, which won't be using the same
global /tmp directory as the server; see bug #825448.

Note that we apply the socket directory change at the level of the
hard-wired defaults in the C code, not by just twiddling the setting in
postgresql.conf.sample; this is so that the change will take effect on
server package update, without requiring any existing postgresql.conf
to be updated.  (Of course, a user who dislikes this behavior can still
override it via postgresql.conf.)


Index: src/include/pg_config_manual.h
===================================================================
--- src/include/pg_config_manual.h.orig
+++ src/include/pg_config_manual.h
@@ -224,7 +224,7 @@
  * support them yet.
  */
 #ifndef WIN32
-#define DEFAULT_PGSOCKET_DIR  "/tmp"
+#define DEFAULT_PGSOCKET_DIR  "/run/postgresql"
 #else
 #define DEFAULT_PGSOCKET_DIR ""
 #endif