Masterlist converter skips some requirement messages.

Requirement messages that contain plugin filenames are reported by
SilentSpike to overwhelmingly be for the plugin's masters, which just
get removed anyway.
Misc. fixes.

* Dirty CRCs are now written out to YAML as hex strings, and plugins
have their dirty info written out.
* Dirty info is now taken into account when checking if a plugin has any
metadata or not.
* Implemented neater string -> hex int conversion.
Fixed masterlist converter bugs.

* File placeholders are now converted without mangling their condition
functions.
* Inversion of conditions now actually works.
Masterlist converter now handles dirty message -> info conversion.

Also skips requirement messages containing plugin filenames, as
according to SilentSpike, the vast majority of these are masters and so
unnecessary.