crecord: add `content` properties to all nodes
In order to have a unified API of what can be searched, let's provide
a `content` property to each node type. This way we can search
filenames, context headers (e.g. containing function names, if
deducible from patch context) or changed lines themselves.
pager.pager=p0 # $TESTTMP/sysrc:4
ui.editor=e1 # $TESTTMP/userrc:2
pager.pager=p2 # $PAGER
ui.editor=e1 # $TESTTMP/userrc:2