Upstream version 6.0.0~rc1+dfsg

Changes:
- Update copyright years for copyright holders
- Drop license & copyright for getopt sources, removed upstream
- Add license & copyright for cpt & mergesort sources

Upstream version 6.0.0~rc2+dfsg

Update to upstream version '6.0.0~rc3+dfsg'
with Debian dir 001bcb17506c372d52066d57ddf7c43d0efbf9f5

Update to upstream version '6.0.0~rc4+dfsg'
with Debian dir 00d97c51c6ea544aacf1331c37fdf877ed726fba

Update to upstream version '6.0.0~rc5+dfsg'
with Debian dir 09a9d20248e565d5c3c085a1a5bdd2861366a390

Update to upstream version '6.0.0~rc5+dfsg1'
with Debian dir bda901621fe224aba8ad05532db3580aad3525ac

This reverts commit 45cb5335.

Update to upstream version '6.0.0+dfsg'
with Debian dir 3d4df496d8f399ba73053649e8c72dd0dc08123c