tests: add test showing that paths outside narrowspec are not added

We had a test that shows that trying to explicitly add a file outside
the narrowspec results in an error, but we didn't have a test that
shows that paths from subdirectories outside the narrowspec are not
added (on e.g. `hg add .`) but silently ignored.

Differential Revision: https://phab.mercurial-scm.org/D4822

tests/test-narrow-commit.t

@@ -53,6 +53,7 b' Can not modify dirstate outside'
   * matcher:
   <includematcher includes='(?:(?:|.*/)f1(?:/|$))'>
   f  inside/f1  inside/f1
+  $ hg add .
   $ hg add outside/f1
   abort: cannot track 'outside/f1' - it is outside the narrow clone
   [255]