MINOR: config: alphanumerically sort config keywords output

MINOR: config: alphanumerically sort config keywords output

The output produced by dump_registered_keywords() really deserves to be
sorted in order to ease comparisons. The function now implements a tiny
sorting mechanism that's suitable for each two-level list, and makes
use of dump_act_rules() to dump rulesets. The code is not significantly
more complicated and some parts (e.g options) could even be factored.
The output is much more exploitable to detect differences now.