index: add a `has_node` method (API)
The new `index.has_node(node)` is to be preferred over:
`node in index.nodemap`.
This get us closer to be able to remove the `nodemap` attribute of the index.
Differential Revision: https://phab.mercurial-scm.org/D7322
#require docutils gettext
Error: the current ro localization has some rst defects exposed by
moving pager to core. These two warnings about references are expected
until the localization is corrected.
$ $TESTDIR/check-gendoc ro
checking for parse errors
gendoc.txt:58: (WARNING/2) Inline interpreted text or phrase reference start-string without end-string.
gendoc.txt:58: (WARNING/2) Inline interpreted text or phrase reference start-string without end-string.