lib/strconv/test/ was the last _test layout deviating from Go's
in-package shape (src/bytes/bytes_test.go declares bytes_test in the
package dir). Its rationale — `import strconv` file-hitting the
sibling strconv.ww — dissolved when #98 made directory packages win
over same-named files on any search entry. libbyteid re-paths the
three fx entries and drops the covered() carve-out: the completeness
scan now keys lib/strconv through the fixtures' dirname. Walk line
flips to "ok lib/strconv [strconv_test, external]".
