fold: improve error messages for multiple heads and roots
This commit adds hints and i18n to the error messages about non-linear
revisions, along with corresponding tests.
recursive-include docs/figures *.svg
include docs/figures/hgview-example.png
include docs/*.rst
include docs/*.py
include docs/tutorials/*.t
include docs/makefile
include docs/static/*.svg
include hgext/__init__.py
include hgext/evolve.py
include hgext/pushexperiment.py
include setup.py
include README
include COPYING
include tests/*.t
include tests/*.py
exclude tests/test-oldconvert.t
exclude tests/test-qsync.t