Log Message:
Update to 0.23.15

Changelog:
    trust: Improve error handling if backed trust file is corrupted [#206]
    url: Prefer upper-case letters in hex characters when encoding [#193]
    trust/extract-jks.c: also honor SOURCE_DATE_EPOCH time [#202]
    virtual: Prefer fixed closures to libffi closures [#196]
    Fix issues spotted by coverity and cppcheck [#194, #204]
    Build and test fixes [#164, #191, #199, #201]