Problem/Motivation
template_preprocess_node() and template_preprocess_comment both call user_view($author, 'compact'); but the compact entity display settings are defined in standard.profile and hence may not exist.
In best case scenario, extra fields are rendered (these are rendered by default for a non-existent display mode).
In worst case scenario, you end up with recursion (#2114887: Maximum nesting level when attaching comment field to User.)
Proposed resolution
Node module comes with a new user view mode (node_author) and configured display mode
Comment modules comes with a new user view mode (comment_author) and configured display mode
Standard profile comes with overrides of the configured display modes and include image field settings for user pictures (comment and node cannot know if image module is enabled in their config).
Upgrade path.
Remaining tasks
Everything
User interface changes
None
API changes
None
Data model changes
New view mode and entity display config objects.
