hooks: print out more information when loading a python hook fails When loading a python hook with file syntax fails, there is no information that this happened while loading a hook. When the python file does not exist even the file name is not printed. (Only that a file is missing.) This patch adds this information and a test for loading a non existing file and a directory not being a python module.

perf: fix perfcca to work with new casecollisionauditor interface A recent changeset, afd75476939e, modified the caescollisionauditor interface but did not update perf.py. This changeset remidies that.

checkheads: extract branchmap preprocessing The checkheads function is far too complicated. This extract help to explicite what part of the preprocessing are reused by the actual check. This the first step toward a wider refactoring.

checkheads: take future obsoleted heads into account If we push some successors they will likely create a new head on remote. However as the obsoleted head will disappear after the push we are not really increasing the number of heads. There is several case which will lead to extra being actually pushed. But this first changeset aims to be simple. See the inline comment for details. Without this change, you need to push --force every time you want to push a newer version which is very error prone. The remote side still display +n heads on unbundle because it does not have the obsolete marker at unbundle time.