Partial fix of hscroll of truncated lines with line numbers

Partial fix of hscroll of truncated lines with line numbers

* src/xdisp.c (x_produce_glyphs, hscroll_window_tree): Adjust
hscroll calculations to line-number display.
* src/term.c (produce_glyphs): Adjust tab stop to window's
hscroll.  These two changes fix horizontal scrolling when line
numbers are displayed.  But there's still a bug: the horizontal
shift of lines that begin with a TAB is different from the rest.
* src/xdisp.c (move_it_in_display_line_to): Call
should_produce_line_number to determine whether a line number
should be produced for this screen line.