Rewrite of Section 12

Rewrite of Section 12 PhL 2.25.12 I am today convinced that C = curl B is a vector density of weight -1, and this means that Section 12 has to be edited somewhat. The main implication is that, for such a vector (see "expansions of tensor..") C = J-1 ΣnC'nen for C = curlB where we have a new J-1 factor sitting there. So I will copy the whole section here and try to edit it. Log of comments and changes. Well, I did the whole thing with a few comments in red. Luckily not a single result changes!! It went pretty fast. Basically all I had to do was replace C'n → J-1 C'n everywhere it appeared, and all changes cancelled out. I think nowadays I could do an "alternative" derivation of the curl in an added section, as I did with the divergence. I will add this at some point, but don't want the huge digression it would require right now. Save it. I think an edit of the vector Laplacian section will be similar to what I have done here. I put that off as well. ________________________________________________________________________________ the rewrite that was right here has now been installed into tensor doc.