now nix-doc-munge will not introduce whitespace changes when it replaces
manpage references with the MD equivalent.
no change to the manpage, changes to the HTML manual are whitespace only.
markdown can't represent the difference without another extension and
both the html manual and the manpage render them the same, so keeping the
distinction is not very useful on its own. with the distinction removed
we can automatically convert many options that use <code> tags to markdown.
the manpage remains unchanged, html manual does not render
differently (but class names on code tags do change from "code" to "literal").
This fixes user environment setup for sessions which doesn't successfully go
through a shell init.
Note we don't go through `sessionVariables` as we want the wrappers to have
highest priority. It would also cause wrapperDir to occur twice when in shell
sessions, as shells use `sessionVariables` too while prepending wrapperDir in a
custom snippet.
In particular logging in and out of gnome-shell could result in a broken path
without this fix.
We were only replacing them in the profiles. We also need to do this in
the values of variables, including both the session-relative variables
and the non-session-relative variables.
