perf: time fncache read and write performance

revset: add "matching" keyword This keyword can be used to find revisions that "match" one or more fields of a given set of revisions. A revision matches another if all the selected fields (description, author, branch, date, files, phase, parents, substate, user, summary and/or metadata) match the corresponding values of those fields on the source revision. By default this keyword looks for revisions that whose metadata match (description, author and date) making it ideal to look for duplicate revisions. matching takes 2 arguments (the second being optional): 1.- rev: a revset represeting a _single_ revision (e.g. tip, ., p1(.), etc) 2.- [field(s) to match]: an optional string containing the field or fields (separated by spaces) to match. Valid fields are most regular context fields and some special fields: * regular fields: - description, author, branch, date, files, phase, parents, substate, user. Note that author and user are synonyms. * special fields: summary, metadata. - summary: matches the first line of the description. - metatadata: It is equivalent to matching 'description user date' (i.e. it matches the main metadata fields). Examples: 1.- Look for revisions with the same metadata (author, description and date) as the 11th revision: hg log -r "matching(11)" 2.- Look for revisions with the same description as the 11th revision: hg log -r "matching(11, description)" 3.- Look for revisions with the same 'summary' (i.e. same first line on their description) as the 11th revision: hg log -r "matching(11, summary)" 4.- Look for revisions with the same author as the current revision: hg log -r "matching(., author)" You could use 'user' rather than 'author' to get the same result. 5.- Look for revisions with the same description _AND_ author as the tip of the repository: hg log -r "matching(tip, 'author description')" 6.- Look for revisions touching the same files as the parent of the tip of the repository hg log -r "matching(p1(tip), files)" 7.- Look for revisions whose subrepos are on the same state as the tip of the repository or its parent hg log -r "matching(p1(tip):tip, substate)" 8.- Look for revisions whose author and subrepo states both match those of any of the revisions on the stable branch: hg log -r "matching(branch(stable), 'author substate')"