upgrade-mycnf doesn't process !includedir

[abg]

The logic exists to track !include/!includedir directives in dbsake.core.mysql.mycnf.parser but the front-end returns the first result and just stops without processing the remaining entries.

This seems to be a simple fix. However, this may break output when --patch is omitted as the current behavior is just to print the modified config on stdout. So that basically output potentially multiple parsed .cnf on stdout which isn't useful - at least with the current "concat" implementation. For now it is probably best to just abort with an error after the first entry if we're not in patch mode, but maybe something smarter can be done in the future (merging configs properly or outputting a tar archive or something along those lines).