Release 1.2.6
spec: Stop building Python documentation
python tests: add missing shebang to run_unittests.sh.in
Make default compression method configurable at build time
doc: Omit modularity-related texts if built without modularity support
Test structured control character validation
Reject illegal characters in un-modifiable fields
1.x specific compatibility code for backporting errors
Strip control characters on package header parse
Fix archive size value for v6 packages
Update Python package build config on 1.x.x-maint