Fix display of Spectral Analysis when no tracks are selected.

Spectral Analysis now displays graphs for selected regions, even when there
are no tracks selected. Fixes #2226.
if auditioner connections are somehow wiped out in CONFIG/ardour.rc, treat them as if they are still "default"
mark the step entry dialog as a dialog even though it is an ArdourWindow, to help with WM layering issues
add -L to curl in linux build script so that 301 responses while fetching harvid are handled
do not include harvid by default in linux build (wrong variable definition)
Merge branch 'master' of git.ardour.org:ardour/ardour