CMP0053: Revise wording and whitespace in policy warning

Write out the behavior change in prose.  Clarify appearance of message
when the input string contains newlines by indenting them too.
ExternalProject: Set LABELS property to targets

This is useful for using CDash subprojects.
ExternalProject: Set FOLDER property to targets

This is useful when using the USE_FOLDERS global property
Merge topic 'ExternalProject_labels' into next

93730bb3 ExternalProject: Set FOLDER property to targets
39ef8046 ExternalProject: Set LABELS property to targets
Merge topic 'dev/faster-evis' into next

3db92087 CMP0053: Revise wording and whitespace in policy warning