fileset: remove subset and unused filtering functions from matchctx

fileset: remove callexisting flag and mctx.existing() (API) They are no longer needed since any files are included as long as they are passed in to the matcher.

fileset: rewrite predicates to return matcher not closed to subset (API) (BC) This makes fileset expression open to any input, so that we can just say "hg status 'set: not binary()'" to select text files including unknowns. With this and removal of subset computation, 'set:**' becomes as fast as 'glob:**'. Further optimization will probably be possible by narrowing the file tree to compute status for example. This also fixes 'subrepo()' to not ignore the current mctx.subset. .. bc:: The fileset expression may include untracked files by default. Use ``tracked()`` to explicitly filter out files not existing at the context revision.

highlight: use matcher API to test if file should be pygmentized Prepares for the upcoming API change. We'll no longer have to call the fileset function directly since the cost of the matcher-based fileset will become O(number of tests) from O(number of files in subset).

fileset: parse argument of size() by predicate function This change is necessary to pass in a size expression to predicatematcher. See the next patch.

fileset: add "tracked()" to explicitly select files in the revision I'm going to rewrite filesets to be match predicates, which means basic patterns such as '*' will no longer be "closed" to the subset constructed from the ctx. Good thing is that 'hg status "set:not binary()"' can include unknown files out of the box, and fileset computation will likely to be faster as we won't have to walk dirstate twice, for example. Bad thing is that we can't select files at a certain revision by 'set:revs(REV, **)' since '**' is "open" to any paths. So, this patch introduces "tracked()" as a replacement for the '**' in the example above.