When in cone mode sparse-checkout, it is unclear how 'git sparse-checkout add <dir1> ...' should behave if the existing sparse-checkout file does not match the cone mode patterns. Change the behavior to fail with an error message about the existing patterns. Also, all cone mode patterns start with a '/' character, so add that restriction. This is necessary for our example test 'cone mode: warn on bad pattern', but also requires modifying the example sparse-checkout file we use to test the warnings related to recognizing cone mode patterns. This error checking would cause a failure further down the test script because of a test that adds non-cone mode patterns without cleaning them up. Perform that cleanup as part of the test now. Reviewed-by: Elijah Newren <newren@gmail.com> Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>