patch: add a new function to initialize diffopts by feature Not all callers are interested in all diffopts -- for example, commands like record (which use diff internally) break when diffopts like noprefix are enabled. This function will allow us to add flags that callers can use to enable only the features they're interested in.

patch.diffopts: use a dict for initialization In upcoming patches we'll conditionally add to and remove from the dict.

largefiles: split the creation of a normal matcher out of its install method Refactoring addremove to support subrepos will need the ability to keep passing the same matcher and narrowing it, instead of monkey patching scmutil's matcher.