- Move PLUGIN_FILE_DESC to common.
- SCH_PLUGIN: rename Load -> LoadSchematicFile, Save -> SaveSchematicFile.
- Use PLUGIN_FILE_DESC and CanRead* in schematic plugins.
- Return none/unknown types from Find/GuessPluginType functions.
- Iterate over file types for file wildcards.
- Clean-up header checking in IO plugins.
- Use PCB plugin list in IO_MGR::GuessPluginTypeFromLibPath.
A sheetpath is required to correctly resolve text variables.
Depending on currentSheet is rife with bugs.
There are many places where we do *not* want to be prepending
field names to the field values, such as netlisting,
building PDF hypertext menus, etc.
Also, Find/Replace needs to work on unresolved text, as
that's what we're going to display (and if replace nuked
your variable references you wouldn't be happy).