A past commit removed the inclusion of redis.h from rdb.c, completely breaking 32 bit builds under Linux.

Ref: issue #103

rioInitWithFile nad rioInitWithBuffer functions now take a rio structure pointer to avoid copying a structure to return value to the caller.

Use a safe iterator while saving the DB, since the getExpire() function will access the iterating dictionary.

INFO now contains the time (in usecs) needed to fork() in order to persist. The info is available in the stats section of INFO.

RDB version signature bumped to 2, now that direct saving of specially encoded types is implemented 2.2 instances are no longer able to read rdb files produced by 2.4 or unstable.

fix type in rdbSaveKeyValuePair() when saving an intset. Don't merge this commit into 2.2 as will not apply cleanly.

save ziplist encoded type as a different type id. Done as separated commit since this is the part that will not merge cleanly in 2.2

fixed two diskstore issues, a quasi-deadlock creating problems with I/O speed and a race condition among threads

touched key for WATCH refactored into a more general thing that can be used also for the cache system. Some more changes towards diskstore working.

Now the rdbSave* functions return the number of bytes written (or
required to write) in serializing a Redis object, writing to /dev/null
and using ftell (which doesn't work on FreeBSD) isn't needed anymore.