Allow excluding files from "Manual synchronization includes"

Not all plugins use the same naming convention for their xml configuration file. Thus an include filter such as

hudson.*xml jenkins*xml *plugin*.xml

doesn't capture all plugin configurations. But if one uses *xml then one also includes credentials.xml. If one lists all plugin xml then one needs to update the filter when installing new plugins. It would be nice if one could specify both an include and an exclude filter so that one could specify:
include: *xml
exclude: credentials.xml