commands: use revlog._deltachain in debugdeltachain We have a nice API now. Use it. This does mean we introduce an extra index lookup for each revision. Considering this is a debug command, the overhead should be acceptable. We could add the chain size to revlog._deltachain(). However, that feels like avoidable overhead.

revlog: refactor delta chain computation into own function This code is already written in multiple locations. While this code needs to be fast and extracting it to its own function adds overhead, code paths reading delta chains typically read, decompress, and do binary patching on revlog data from the delta chain. This other work (especially zlib decompression) almost certainly accounts for a lot more time than the overhead of introducing a Python function call. So I'm not worried about the performance impact of this change.

perf: call clearcaches() in perfmanifest The old code only partially cleared the caches. Now that we have a comprehensive method for wiping all caches, let's call it. This appears to introduce a marginal regression in `hg perfmanifest` on mozilla-central. This is good because the new result is more accurate since caches aren't being used.

manifest: implement clearcaches() The manifest implements its own caches in addition to revlog's. Extend the base clearcaches() to wipe these as well.

revlog: make clearcaches() more effective clearcaches() was added several years ago in e8d37b78acfb as part of implementing a perf command. Since revlog instances have many caches and since the spirit of this mostly unused method is to facilitate performance testing, I think it's appropriate for all the revlog's caches to get cleared when it is called.

fileset: detect unintentional existing() invocation at runtime A fileset predicate can invoke 'matchctx.existing()' successfully, even if it isn't marked as "existing caller". It is aborted only in some corner cases: e.g. there were one deleted file in the working directory (see 8a0513bf030a for detail). This patch makes 'matchctx.existing()' invocation abort if not '_existingenabled', which is true only while "existing caller" running. After this changes, non-"existing caller" predicate function is aborted immediately, whenever it invokes 'matchctx.existing()'. This prevent developer from forgetting to mark a predicate as "existing caller". BTW, unintentional 'matchctx.status()' invocation can be detected easily without any additional trick like this patch, because it returns 'None' if a predicate isn't marked as "status caller", and referring field (e.g. '.modified') of it is always aborted.

fileset: use set instead of list to mark predicates for efficiency (API) This reduces cost of examining whether given predicate calls 'matchctx.status()' or 'matchctx.existing()' in 'getfileset()' at runtime. This kind of examination is used also in subsequent patch, which detects unintentional 'matchctx.existing()' invocation per each predicate evaluation.