patch: rename diffopts to diffallopts This is meant to be used when all features are explicitly requested. diffopts is kept as an alias for now -- it will go away soon.

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.