[sqlite] Fix integrity error parsing
Up to sqlite 3.7, integrity error message may be in the singular form
if only one column is in the unique index.
Closes #5224632
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html