fileset: add grep predicate

fileset: add some function help text

fileset: add hgignore

fileset: add resolved and unresolved predicates

fileset: prescan parse tree to optimize status usage We only call status if needed to avoid walking the working directory or comparing manifests. Similarly, we scan for whether unknown or ignored files are mentioned so we can include them.

fileset: add support for file status predicates This forcibly walks the tree looking for unknown and ignored files, which is suboptimal. A better approach would scan the tree first to find required status components and skip the status check entirely if it's unused.

fileset: add some basic predicates

match: introduce basic fileset support

match: allow passing a context object to match core

fileset: drop matchfn This is now built into contexts