bugfix: schemas/util.sql: diff_views(): need to use $2, not $1, for the 2nd query

fix: schemas/util.sql: materialize_query(): remove any extra blank line before the query, to improve readability when newlines are used as a log message separator and are therefore confusing in the middle of a log message

schemas/util.sql: added ltrim_nl()

bugfix: schemas/vegbien.sql: setting search_path locally: also need to set function option search_path, in order to limit the effects of `SET LOCAL search_path` (mk_set_search_path()) to the current function (http://www.postgresql.org/docs/9.1/static/sql-set.html#AEN75423)

bugfix: schemas/vegbien.sql: setting search_path locally: need to use `SET LOCAL search_path TO` instead of `PERFORM set_config(search_path, ..., is_local := true)` because the meaning of is_local refers to the entire transaction, not just the current function (as for LOCAL)

schemas/util.sql: added mk_set_search_path(VARIADIC schemas text[])

schemas/util.sql: added mk_use_own_schema()

schemas/util.sql: added mk_set_search_path()

schemas/util.sql: use builtin string_agg(..., ) instead of concat()

schemas/util.sql: added qual_name(type unknown) to avoid needing to explicitly specify the type of an input string