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>

The latest version of qwt does have these warnings fixed. But the
latest version also has removed some deprecated printing functionality
which we are currently using. I gave a try at updating but it looked
fairly involved and over my level of understanding for that part of the
code. So pragmas for now. When someone does upgrade qwt the pragmas
will no longer be needed.

The latest version of qwt does have these warnings fixed. But the
latest version also has removed some deprecated printing functionality
which we are currently using. I gave a try at updating but it looked
fairly involved and over my level of understanding for that part of the
code. So pragmas for now. When someone does upgrade qwt the pragmas
will no longer be needed.

Put libraries into one libs directory under qgroundcontrol. Changed the neccessary files with references to those libraries.