narrow: move .hg/narrowspec to .hg/store/narrowspec (BC) The narrowspec is more closely related to the store than to the working copy. For example, if the narrowspec changes, the set of revlogs also needs to change (the working copy may change, but that depends on which commit is checked out). Also, when using the share extension, the narrowspec needs to be shared along with the store. This patch therefore moves the narrowspec into the store/ directory. This is clearly a breaking change, but I haven't bothered trying to fall back to reading the narrowspec from the old location (.hg/), because there are very few users of narrow out there. (We'll add a temporary hack to our Google-internal extension to handle the migration.) Differential Revision: https://phab.mercurial-scm.org/D4099