fix for wrong preposition tag

Fix for issue https://github.com/opencog/relex/issues/82


without unit test cases, its hard for me to say ... 

Can you also add a unit test for the shorter sentence "There were 769 households of which 38.5% had children" and check for the absence of the pronoun tag?

Also:  not that two, lines above, there is a <LAB> = \MX.j\.*|\Mj\.*   so when you say LAB> != \Mj you are just undoing the earlier match to Mj ...   So, since someone once wrote \MX.j\.*|\Mj\.*  They must have really meant to include the Mj there .. but without example sentences I don't know why ...