memcached: updated to 1.5.17

1.5.17:
Fixes
fix strncpy call in stats conns to avoid ASAN violation
extstore: fix indentation
add error handling when calling dup function
add unlock when item_cachedump malloc failed
extstore: emulate pread(v) for macOS
fix off-by-one in logger to allow CAS commands to be logged.
use strdup for explicitly configured slab sizes
move mem_requested from slabs.c to items.c (internal cleanup)

New Features
add server address to the "stats conns" output
log client connection id with fetchers and mutations
Add a handler for seccomp crashes

(adam)