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pax allows each letter to be in the xattr value only once, so
create the value accordingly. This also keeps the letters sorted
in the xattr value which is useful for apk in various ways.

rebase libcap patch, and add speexdsp-dev dependency due to
recent package split.

issue with _POSIX_PRIORITY_SCHEDULING reported upstream:
https://github.com/luaposix/luaposix/issues/223

A lot of gtk3 fixes, but also biblesync got split out.

biblesync was the navigation/IPC part of Xiphos, but has now been split
off into a public library.