parser: add stub class that will host alias parsing and expansion This class will keep syntax rules that are necessary to parse and expand aliases. The implementations will be extracted from the revset module. In order to make the porting easier, this class keeps parsedecl and parsedefn separately, which will be unified later. Also, getlist and funcnode will be refactored by future patches for better handling of the template aliases. The following public functions will be added: aliasrules.build(decl, defn) -> aliasobj parse decl and defn into an object that keeps alias name, arguments and replacement tree. aliasrules.buildmap(aliasitems) -> aliasdict helper to build() a dict of alias objects from a list of (decl, defn) aliasrules.expand(aliasdict, tree) -> tree expand aliases in tree recursively Because these functions aren't introduced by this series, there would remain a few wrapper functions in the revset module. These ugly wrappers should be eliminated by the next series. This class is considered an inheritable namespace, which will host only class/static methods. That's because it won't have no object-scope variables. I'm not a big fan of using class as a syntax sugar, but I admit it can improve code readability at some level. So let's give it a try.

revset: narrow scope of "except ParseError" block in _parsealiasdecl() This helps to factor out a common function. "if True" will be removed soon.

obsstore: move delete function from obsstore class to repair module Since one of the original patches was accepted already and people on the mailing list still have suggestions as to how this should be improved, I'm implementing those suggestions in the following patches (this and the ones that might follow).

debugobsolete: style fixes to debugobsolete that slipped from original commit

import: document --exact behavior in more detail

util: add doctest to datestr()

date: fix boundary check of negative integer