comment connector:store iterator to src

ie unstead of the 'thing which connects comments to souce text' storing
the source text, it now just stores (client accesable) iterators to the
source text, stored seperately.

Why client accesibly? To avoid iterator/const_iterator mismatch.
clumsy, but gracefull... (and enables Ikkur Tosfos Yom Tov)

this was an absurdly anourmous change done late at night, whith no
problems, B"H !! If that isn't an open miracle, I don't know what is.