Merge branch 'maint-1.6.0' into maint-1.6.1

* maint-1.6.0: base85: Make the code more obvious instead of explaining the non-obvious base85: encode_85() does not use the decode table base85 debug code: Fix length byte calculation checkout -m: do not try to fall back to --merge from an unborn branch branch: die explicitly why when calling "git branch [-a|-r] branchname".