qreal is a double on some platforms (x86) and a float on others (e.g. ARM), cast it to fix build errors like these:

src/ui/designer/QGCXYPlot.cc: In member function 'int
XYPlotCurve::appendData(const QPointF&)':
src/ui/designer/QGCXYPlot.cc:41:39: error: no matching function for call
to 'qMin(double&, qreal)'
             xmin = qMin(xmin, data.x());
                                       ^
src/ui/designer/QGCXYPlot.cc:41:39: note: candidate is:
In file included from
/build/v2013.12/build/tmp-angstrom_v2013_12-eglibc/sysroots/sama5d3_xplained/usr/include/qt4/QtCore/qnamespace.h:45:0,
                 from
/build/v2013.12/build/tmp-angstrom_v2013_12-eglibc/sysroots/sama5d3_xplained/usr/include/qt4/QtCore/qobjectdefs.h:45,
                 from
/build/v2013.12/build/tmp-angstrom_v2013_12-eglibc/sysroots/sama5d3_xplained/usr/include/qt4/QtGui/qwindowdefs.h:45,
                 from
/build/v2013.12/build/tmp-angstrom_v2013_12-eglibc/sysroots/sama5d3_xplained/usr/include/qt4/QtGui/qwidget.h:46,
                 from
/build/v2013.12/build/tmp-angstrom_v2013_12-eglibc/sysroots/sama5d3_xplained/usr/include/qt4/QtGui/qdockwidget.h:45,
                 from
/build/v2013.12/build/tmp-angstrom_v2013_12-eglibc/sysroots/sama5d3_xplained/usr/include/qt4/QtGui/QDockWidget:1,
                 from src/ui/designer/QGCXYPlot.cc:1:
/build/v2013.12/build/tmp-angstrom_v2013_12-eglibc/sysroots/sama5d3_xplained/usr/include/qt4/QtCore/qglobal.h:1213:34:
note: template<class T> const T& qMin(const T&, const T&)
 Q_DECL_CONSTEXPR inline const T &qMin(const T &a, const T &b) { return
(a < b) ? a : b; }
                                  ^

See http://www.qtcentre.org/archive/index.php/t-45475.html for some
background.

This fixes #625
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>

This reverts commit af0589b2.

Fix execution context of thread routines - note that this is not quite the architecture the Qt folks intended, but as they admit its the consequence of their architecture.

Avoid evil port config for CDC devices altogether, non-CDC devices (unknown devices) should be unaffected

Do not configure the port if talking to PX4 units (since USB does not know anything about baud rate)

Removed completely unused variables. Ifdef’ed out variable which is
referenced from commented out code.