A using-directive or using-declaration in the global namespace of a
header reaches every file that includes it, and a using-declaration also
makes the include checker treat that header as the one to include for
the name. google-global-names-in-headers reports both, on changed lines
like the existing check, so headers that still have one are not held to
it until the line is touched.
The check does not see a using inside a namespace.
clang_tidy_diff.py's closing message assumed every finding was a missing
include; it now says other findings need a manual fix.
Hanif Koh
7412dab76a