Fix incorrect check for tab size validity.

Fix a bug where an interrupted read that was continued discarded the …

…result of conversion.

Fix build on C++14 and later compilers

Require libt3widget 1.2.0 or later for explicit negation

Update changelog for new release

Update Changelog for release

Fix broken code

Check that the file that was opened for read-write is the same as the…

… one that was opened read-only.

Fix most of the testsuite

Merge branch 'master' into abi-breaking-changes

Using strategy ours, to allow merging this branch into master to replace it.