The same Manchester development company that bought the Franklin Street mill property in Nashua to turn it into housing has also spent more than $17 million in the past two months to buy up about half a million square feet of additional commercial and industrial space in Nashua and Hudson. Brady Sullivan Properties acquired about 1 million square feet of commercial and industrial space in Greater Nashua, Manchester and Concord in the last two months in a move the Manchester-based real estate development firm said would expand its presence in southern New Hampshire.