fileset: build status according to 'withstatus' hint _switchcallers is no longer needed since 'withstatus' node is reinserted for arguments of functions like revs(). New matchctx instance is created per 'withstatus' to make sure that status tuple is available only for children of the 'withstatus' node.

fileset: insert hints where status should be computed This will allow us to compute status against a narrowed set of files. For example, "path:build/ & (unknown() + missing())" is rewritten as "path:build/ & <withstatus>(unknown() + missing(), 'unknown missing')", and the status call can be narrowed by the left-hand-side matcher, "path:build/". mctx.buildstatus() calls will be solely processed by getmatchwithstatus().