Internal helper locating a README regardless of capitalization or
extension. Any file whose stem matches readme counts: README.md,
readme, Readme.pdf, and README.tex all match. A directory named
readme does not, nor does readme-old.md, nor a double extension such
as readme.tar.gz.
Value
The full path to the first matching file, or NULL when the
directory holds none or does not exist.
Details
Shared by init_project(), which refuses to write a README over one that
already exists, and check_project(), which reports whether the project
has one. Before this helper existed the two disagreed: check_project()
matched any variant while init_project() checked one exact filename, so
a project holding readme.txt would quietly acquire a second README.md
beside it.