Redis/Jemalloc Gitignore were too aggressive.

Redis gitignore was too aggressive since simply broken.

Jemalloc gitignore was too agressive because it is conceived to just
keep the files that allow to generate all the rest in development
environments (so for instance the "configure" file is excluded).
Cluster: fix clusterNode.name print format on debug message.

It was %40s instead of %.40s, and since the string is not null
terminated it caused random garbage to be displayed, and possibly a
crash.
More explicit panic message on out of memory.
Sentinel: turn old master into a slave when it comes back.