[IMP] l10n_es_aeat: Don't split regularization lines for same account. Closes #305
[IMP] l10n_es_aeat: Don't split regularization lines for same account. Closes #305

If some tax lines have to been regularized, and they have the same account, previous
to this commit, they appear in separate lines. Now, all are merged in only one line
(if the balance sign is the same).

cubells/l10n-spain,cubells/l10n-spain,cubells/l10n-spain