hgweb: add revset syntax support to search This mode is used when all the conditions are met: - 'reverse(%s)' % query string can be parsed to a revset tree - this tree has depth more than two, i.e. the query has some part of revset syntax used - the repo can be actually matched against this tree, i.e. it has only existent function/operators and revisions/tags/bookmarks specified are correct - no revset regexes are used in the query (strings which start with 're:') - only functions explicitly marked as safe in revset.py are used in the query Add several new tests for different parsing conditions and exception handling.

revset: add a whitelist of DoS-safe symbols 'Safe' here means that they can't be used for a DoS attack for any given input.

revset: add helper function to get functions used in a revset parse tree Will be used to determine whether all functions used in a hgweb search query are allowed there.

revset: add helper function to get revset parse tree depth Will be used to determine if a hgweb search query actually uses any revset syntax.

parsers: use a lookup table to convert hex to binary This is a hotspot for parse_manifest. With this patch, for a 20 MB, 200,000 file manifest, parse_manifest goes down from 0.153 seconds to 0.116.

revlog: remove _chunkbase since it is no longer used This was introduced in 2011 for the lwcopy feature but never actually got used. A similar hook can easily be reintroduced if needed in the future.

revlog: move chunk cache preload from revision to _chunks In case we don't have a cached text already, add the base rev to the list passed to _chunks. In the cached case this also avoids unnecessarily preloading the chunk for the cached rev.