gitk: Skip over AUTHOR/COMMIT_DATE when searching all fields
gitk: Skip over AUTHOR/COMMIT_DATE when searching all fields

This prevents a search for a number like "105" on "All Fields" from
matching against the raw author and commit timestamps.  These
timestamps were already not searchable by themselves, and the
displayed format does not match the query string anyway.

Signed-off-by: Frédéric Brière <138584a8b44c8500926cbe73211e2823dae3b65e@fbriere.net>
Signed-off-by: Jonathan Nieder <b57189c5f2fd5b3daf3350a77fde90def1080fa5@gmail.com>
Signed-off-by: Paul Mackerras <19a0ba370c443ba08d20b5061586430ab449ee8c@samba.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git