update to 5.7
only build & install library & headers
configure with --prefix=/usr so library (newterm() at least) will look
at installed terminfo database (ncurses interface wouldn't work on OSX)

type is void and not boolean (assert failed in var_SetChecked)

This is not really relevant as long as we have only one item.
However, sout-keep should really always be on anyway when streaming.
Most protocols would terminate client connections when the item
changes, and the file output would overwrite the file.

(sout_gather would be more problematic. We should use it too, but it
has always made sout_display crash.)

Reusing settings from before 1.1.0 results in a mess.

We don't use GLX with Xomap (rather XV or X11)

In 0.9, the output refuses to work and the codec just segfaults.
In 1.0, it is inoperant due to the removal of the forked libmpeg2.
In 1.1, we would anyway need to rewrite it to the new vout API.

GLX does not use SysV shared memory directly.

This smells like fishy cut&paste from the former XV plugin.

Keeps previous behavior when subtitles overlapped in time,
except when trying to move subtitles below the bottom picture edge
-> they start to visually overlap because of bounding.

This reverts commit 4c627dc6.

Fixes the glitch when displaying subtitles and subtitle position != 0.
Modifies behavior when subtitles overlap: newer subtitles push older ones higher