display the pagetitle() in linkmaps

display the pagetitle() in linkmaps

without this patch, linkmaps display underscores and underscore escape
sequences in the rendered output.

this introduces a pageescape function, which invoces pagetitle() to get
rid of underscore escapes and wraps the resulting utf8 string
appropriately for inclusion in a dot file (using dot's html encoding
because it can represent the '\"' dyad properly, and because it doesn't
need special-casing of newlines).