storageutil: extract most of emitrevisions() to standalone function As part of implementing a storage backend, I found myself copying most of revlog.emitrevisions(). This code is highly nuanced and it bothered me greatly to be copying such low-level code. This commit extracts the bulk of revlog.emitrevisions() into a new standalone function. In order to make the function generally usable, all "self" function calls that aren't exposed on the ifilestorage interface are passed in via callable arguments. No meaningful behavior should have changed as part of the port. Upcoming commits will tweak behavior to make the code more generically usable. Differential Revision: https://phab.mercurial-scm.org/D4803

storageutil: invert logic of file data comparison IMO things make more sense when the function is explicitly a test for file data equivalence. Not bothering with API since the function was introduced by the previous commit. Differential Revision: https://phab.mercurial-scm.org/D4802

storageutil: extract filelog.cmp() to a standalone function As part of implementing an alternate storage backend, I found myself reimplementing this code. With a little massaging, we can extract filelog.cmp() to a standalone function. As part of this, the call to revlog.cmp() was inlined (it is just a 2-line function). I also tweaked some variable names to improve readability. I'll further tweak names in a subsequent commit. Differential Revision: https://phab.mercurial-scm.org/D4801

storageutil: extract copy metadata retrieval out of filelog As part of implementing an alternate storage backend, I found myself reinventing this wheel. Let's create a utility function for doing the work. Differential Revision: https://phab.mercurial-scm.org/D4800