Search fields can be overridden again. Fixes #709
Fixed login form to reference USERNAME_FIELD

Was hardcoded to say 'username' when USERNAME_FIELD may be 'email' etc.
Updated LoginForm to dynamically set placeholder text

Placeholder text is now determined from the verbose name of AUTH_USER_MODEL's USERNAME_FIELD
Merge branch 'master' into custom-user-model-fixes
Merge branch 'master' into custom-user-model-fixes

Conflicts:
	wagtail/wagtailadmin/forms.py
Merge branch 'master' into custom-user-model-fixes
Added back 'your'
Added get_indexed_instance method

When a signal handler is run on a model that is the parent in a multi
table inheritance relationship, we do not have access to all of the
fields we need to properly reindex the object.

This commit adds a method that the developer can use to specify how to
get the specific type of a particular instance which we can use to
reindex it.
Merge pull request #705 from jsma/custom-user-model-fixes

Fixed login form to reference USERNAME_FIELD
Changelog for #705
Changelog for #705
Release note for #705
Merge branch 'search/index-correct-object' of https://github.com/kaedroho/wagtail into kaedroho-search/index-correct-object
Merge branch 'kaedroho-search/index-correct-object'
fix spelling
Merge branch 'search/search-fields-overriding' of https://github.com/kaedroho/wagtail into kaedroho-search/search-fields-overriding
add clarifying comment about how test_overriding relates to model inheritance
Prevent search signal handlers from breaking fixture loading on Django 1.7
release note for #715
Merge branch 'kaedroho-search/search-fields-overriding'