remove spaces from META['HTTP_X_FORWARDED_FOR'] as throttle key

memcached cannot handle spaces in keys
Update throttling.py

python 3 u'' gone
Use help_text, verbose_name, editable attributes for related fields
Do not check model_field's attributes if it is None
Metadata for related fields -- added test case.
Stray unicode string marker removed
Allow customising ChoiceField blank display value
Merge remote-tracking branch 'upstream/master'

Conflicts:
	rest_framework/tests/models.py
Sync test result w/ new label
Added help_text to expected response in test
Merge pull request #1409 from tuky/patch-1

remove spaces from META['HTTP_X_FORWARDED_FOR'] as throttle key
Mark strings in AuthTokenSerializer as translatable
Fix missing message in ValidationError
Automatically set the field name as value for the HTML `id` attribute on the rendered widget.
Added missing "to" word
Added missing "the" word
Removed superfluous "./"s
Merge pull request #1567 from sbellem/help-docs

Help docs
Merge pull request #1561 from incuna/i18n

Mark strings in AuthTokenSerializer as translatable
Merge pull request #1485 from Atrasoftware/master

Use help_text, verbose_name, editable attributes for related fields