Advanced search : set default logical operator to "OR" when adding new line

[mmercapi]

Current situation
In an advanced search, default behaviour of adding a new line of "reference" or "choice sets" fields, is an "AND" operator associated to the new line, resulting in too often default empty results list.

Suggestion
Setting default logical operator "OR" for new lines might avoid unsucessful searches for unexperimented users. Furthermore, "the AND" operator option should be completely removed for "reference" and "choice sets" new lines (no added value compared to "OR").