hgweb: better names for _navseq arguments The old names were misleading.

hgweb: drop recursivity in _navseq This is totally not needed.

hgweb: move the `seq` function out of the revnavgen scope There is not reason for it to be a in there. And this function could use a major reworks.

hgweb: simplify return value creation in for navgen We now have access to better syntax allowing a clearer version.

hgweb: do not access first changeset with a string There is not reason not to use an int

refactoring: use unlinkpath with ignoremissing

docs: "deprecate" checkchanged and checkconflicts in merge-tool configuration These settings were replaced by check=changed and check=conflicts in a912f26777d3. There is no reason to announce two different ways to achieve the same. The old way should be kept but not announced.

tests: run with PYTHONHASHSEED=random Python set and dict iteration order is in principle undefined but usually 'quite stable'. Setting PYTHONHASHSEED=random will make the iteration order more random in Python 2.6.8 and 2.7.3 and where it has been backported. This can thus help spot dependencies on undefined behaviour and prevent future problems.