Minor fixes to make 2.8.0 work on OSX

Remove locale check
Prevent disabling GUI or keyboard input is no longer registered after
running experiment
Bump to 2.8.1~pre1
Do not choke on translations in font-selection dialog
Updated debian/changelog
Flush buffers *before* sending stop/start byte.
Merge remote-tracking branch 'rsprouse/master' into playground
Systematic validation of conditional statements (#235)
- Some code cleanup
- Some unicodification
Sort item comboboxes alphabetically (#233)
Sort items alphabetically in OpenSesame script (#236)
Default to 'never' for loop break-if statements
Update debian/changelog
Improve event handling of script changes.
- Temporary fix until #219 is properly implemented.
Convert `text_display` plug-in to new-style API
- Use HTML renderer
- Deal with os-specific line separators (closes #237)
Cleanup sampler.legacy
- Unicodify
- Flush the keyboard while waiting (closes #227)
Convert `print` statements to Python-3-compatibile `print()` function calls
Convert `reset_feedback` plug-in to new style plug-in API.
Use initial value for jitter_mode in advanced_delay plug-in (closes #238)
Update debian/changelog
Merge remote-tracking branch 'upstream/master'