Backend support for streaming base backups

Add BASE_BACKUP command to walsender, allowing it to stream a
base backup to the client (in tar format). The syntax is still
far from ideal, that will be fixed in the switch to use a proper
grammar for walsender.

No client included yet, will come as a separate commit.

Magnus Hagander and Heikki Linnakangas

src/include/replication/basebackup.h

@@ -0,0 +1,17 @@
+/*-------------------------------------------------------------------------
+ *
+ * basebackup.h
+ *	  Exports from replication/basebackup.c.
+ *
+ * Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
+ *
+ * src/include/replication/walsender.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef _BASEBACKUP_H
+#define _BASEBACKUP_H
+
+extern void SendBaseBackup(const char *options);
+
+#endif   /* _BASEBACKUP_H */