v0.19.3

Fixed

• extends path validation means the same thing on every host. The guards that keep an
  extends source's file inside the base checkout were written against std::path,
  which parses per-platform: /etc/passwd is rooted but not absolute on Windows, so
  is_absolute() accepted it there, while C:\Windows\system.ini, \\server\share\x
  and a\..\b are an ordinary filename and a single component on Unix and were accepted
  here. file is portable config resolved inside a checkout, so it is now inspected as a
  string: POSIX roots, UNC roots and drive qualifiers (including the drive-relative C:x)
  are rejected everywhere, as is a .. segment separated by either slash. This was
  failing ci on the windows runner.