Append/prepend commands. Introduce new storage commands "append" and "prepend" for atomic value modification. They follow generic storage commands interface as described in doc/protocol.txt: <command name> <key> <flags> <exptime> <bytes>\r\n <data block>\r\n Current implementation involves memcpy() twice to combine values on writing (i.e. full resulting value are copied), but truly atomic (and even threadsafe).

--- a/memcached.h
+++ b/memcached.h
@@ -134,6 +134,8 @@ enum conn_states {
 #define NREAD_ADD 1
 #define NREAD_SET 2
 #define NREAD_REPLACE 3
+#define NREAD_APPEND 4
+#define NREAD_PREPEND 5
 
 typedef struct {
     int    sfd;