narrow: mark wire proto capability names experimental and versioned We already plan to add a "widen" wire protocol command to the "narrow" capability, so let's version the capabilities as "exp-narrow-1" and "exp-ellipses-1". When we add the "widen" command, we will then add a "exp-narrow-2" capability to indicate support for that command. Differential Revision: https://phab.mercurial-scm.org/D4529