Patch 659834 by Magnus Lie Hetland:

Check for readline 2.2 features.  This should make it possible to
compile readline.c again with GNU readline versions 2.0 or 2.1; this
ability was removed in readline.c rev. 2.49.  Apparently the older
versions are still in widespread deployment on older Solaris
installations.  With an older readline, completion behavior is subtly
different (a space is always added).