Change to @@=str_format in l3str-format.

In this same commit, introduce \@@_if_in:nNTF, which
behaves like l3str's \__str_if_contains_char:nNTF,
hoping to remove this weird internal function from
l3str eventually, or find a better approach there.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4404 de43f980-851b-0410-b2f7-c40aca1f87e0
Fix copyright info


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4405 de43f980-851b-0410-b2f7-c40aca1f87e0