merge with stable

changelog: announce that obsfate is hg > 4.2 now Update changelog to announce the fact that obsfate has been improved and is now only compatible with mercurial version greater than 4.2.

compat: make obshistory._getdifflines compatible with mercurial 4.1 On Mercurial version 4.1 and lower, patch.diff seems to returns an empty list when there is no change. Mercurial 4.2 returns None so we add a if for this case.

obsfate: add a new obsfate template The obsfate template display for each obsolete changeset a line summarizing what changed between the changeset and its successors. This dict is computed in obshistory._preparesuccessorset. It uses obshistory.FORMATSSETSFUNCTIONS which is a list of function that individually compute a part of each dict. You can override fields or add new ones by adding your own function in this list. The format of obsfate is computed in templatekw.obsfatedefaulttempl and can be wrapped if necessary, the code is not quite extendable for the moment but can be refactored later.

obsfate: prepare fatelog tests Prepare obsfate venue by adding new blank output, it will helps clarify which are the new output due to obsfate or not.

obsfate: build more advanced markers for tests Prepare obsfate venue by building more advanced markers by varying obs markers users and dates.

readme: fix entry for 6.4.0 some data were missing and some were in the wrong spot