Fixed a minor bug in GETSET, now the SET part is not performed if the GET fails because the key does not contain a string value

SHUTDOWN now does the right thing when append only is on, that is, fsync instead to save the snapshot.

LZF compression re-enabled by default, but with INIT_HTAB set to 0 to avoid the very costly memset initialization. Note that with this option set valgrind will output some false positive about lzf_c.c

Two important fixes to append only file: zero length values and expires. A pretty neat new test to check consistency of randomly build datasets against snapshotting and AOF.

Fixed some subtle bug in the command processing code almost impossible to spot in the real world, thanks to gcov