Low: rethink sed command complexity vs. compatibility trade-off
This change effectively reverts [8ebeb52] and re-does the intended
compatibility enhancement in a less intrusive (and hopefully more
compatible) way + the same is applied at another instance of
'BRE-imposed, ERE-unsupported backslashing of meta-plus'.
Note that there is a counter-proposal by Ken:
https://github.com/ClusterLabs/pacemaker/pull/938
It is expected that -E switch will eventually become fully adpoted by
main "sed" implementations, but at this point it seems unwise to drop
backward compatibility (with up to at least ~2008 POSIX) altogether:
http://austingroupbugs.net/view.php?id=528
https://github.com/ClusterLabs/pacemaker/pull/861#commitcomment-16356114