Normalize newlines in DjVu text-layer metadata.

Currently, newlines in DjVu text layer are stored as the literal
string '\n'. Its up to the consumer to unescape that into
a real newline. Other formats like pdfs return newlines
as an actual \n character when getPageText() is called.
I think getPageText() should not require callers to do this.

Change-Id: Ie1a438bbce5444c53ff6b7b3aaf2b5267ba3c8b4
Merge "Normalize newlines in DjVu text-layer metadata."