Misc ignore-related project.el changes

* lisp/progmodes/project.el (project-ignores): Don't append the
default ignores list, just use vc-directory-exclusion-list.
(project--dir-ignores): Use the default ignores if the dir is
outside of the current project.
(project-files): Use project--dir-ignores to support external
roots better.
1 job for master in 50 minutes and 1 second (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #593
test-all

00:50:01