bug fix: existing keywords are not checked properly.
the grep is checking a regex against arrayrefs.
(fixing this bug breaks t/plugin_syntax.t since it's
causing 2 registrations of the same keyword - to be fixed)
changed dsl_keywords to hashref, managing a key/value pair structure
in AoA doesn't make much sense, and bug in checking existing keys
(fixed in a23012b47) made it possible to re-register the same keyword
even with a different (is_global) value which may lead to unexpected
behavior.
(t/plugin_syntax.t is still broken)
added missing anchors to regexp built with prefix
removed a redundant trigger sub that does nothing.
session id --> 'ro'