bundlespec: move computing the bundle contentops in parsebundlespec We will introduce a new bundlespec for stream bundle which will influence the contentops. Differential Revision: https://phab.mercurial-scm.org/D1952

bundlespec: introduce an attr-based class for bundlespec We will add support of contentops in the next patch, introduce a class instead of returning a 4-items tuple. Differential Revision: https://phab.mercurial-scm.org/D2971