Address book file backend will break with error message, if required

Address book file backend will break with error message, if required
address book fields are not available. Prevents address book corruption
and address book format violations that can cause PHP notices.

Added line length setting in local_file address book backend (#1181561).

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@11311 7612ce4b-ef26-0410-bec9-ea0150e637f0