lazyparser.findnode: fix typo and s/rfind/find/ There's no reason to use reverse string search and it's slightly slower

lazyindex: speed up __getitem__ This function is fairly performance sensitive, so we make a couple ugly tweaks: - keep all entries packed so we needn't test entry types - fold index lookup/load into unpack call to eliminate local variable setting

lazyparser: up the blocksize from 512 bytes to 64k

revlog: implement a fast path for heads

revlogio: speed up parsing - precalcuate ending offset - pull some variables into local scope - separate inline and out of line code paths

revlog: eliminate diff and patches functions call mdiff variants directly

revlog: speed up chunkcache - use a reasonable cache size - avoid an extra copy when we pull in big revs

revlog: some basic code reordering

revlog: abstract out index entry packing This lets us remove most of the remaining v0/v1 logic from revlog

revlog: simplify revlog.__init__ - move stat into io helper - get rid of self.defversion and self.indexstat - fold _load into __init__