extdiff: pass full paths of `dir1a` and `dir1b` to `_runperfilediff()` Earlier we were passing basename instead of the fullpath and then joining with the tmproot. This is wrong because the user can choose `rev1a` as wdir and in those cases, tmproot should not be joined with the path. I am working on refactoring extdiff logic so that we can have options like `diff --tool` and encountered this. Although this patch in itself makes no difference, however in future when a new caller of `_runperfilediff()` will be added, it will be useful to directly pass on the full paths instead. Differential Revision: https://phab.mercurial-scm.org/D8969