extensions: gracefully warn when doing min version check with no local version
After doing a `make clean`, I started getting cryptic failures to import
extensions with the `minimumhgversion` attribute on py3:
*** failed to import extension evolve: '>' not supported between instances of 'int' and 'NoneType'
*** failed to import extension topic: '>' not supported between instances of 'int' and 'NoneType'
This now handles the `(None, None)` tuple before comparing, and disables the
extension with the same friendly message as in py2.
Differential Revision: https://phab.mercurial-scm.org/D9363
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1