externalprocess: Hotfix: Ignores stdin write errors.

Re: ArchiveTeam/seesaw-kit#55, ArchiveTeam/seesaw-kit#48.
Bumps version to 0.1.6b1.
externalprocess.py: Catches exit status 0 but with stdin error as error.
Version 0.1.6.

Merge branch 'development'

Conflicts:
	seesaw/__init__.py
Merge branch 'master' into python3/development

Conflicts:
	seesaw/__init__.py