docs: improve discoverability of exclude pathspec
The ability to exclude paths with a negative pathspec is not mentioned
in the man pages for git grep and other commands where it might be
useful.
Add an example and a pointer to the pathspec glossary entry in the man
page for git grep to help the user to discover this ability.
Add similar pointers from the git-add and git-status man pages.
Additionally,
- Add a test for the behaviour when multiple exclusions are present.
- Add a test for the ^ alias.
- Improve name of existing test.
- Improve grammar in glossary description of the exclude pathspec.
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Manav Rathi <mnvrth@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>