SciDAVis - Improvements SVN-temp

- Added sanity check to Graph::updateCurvesData(). If one of the columns of a
DataCurve changes type, remove the curve instead of crashing when trying to
update the axis format in DataCurve::loadData(). Closes bug #2802185.

- fixed bug #2802095: Crash when adding error bars with empty columns

- Changed file saving on Windows to remove files before replacing them, since
Windows doesn't support atomic rename. Closes bug #2797508.

- Added some sanity checks to prevent crashes when trying to plot from invalid
table/column using Python.

- Added planck_wavelength fit plugin.

- Some build system fixes for building on MacOS X Tiger.
- Fixed small type on scidavis.pro.

- fixed bug #2794038: Limitation in matrix coordinate - Last column X

- added mathematical minus sign to the symbol table

- Fixed compilation with Qwt 5.2.0.

- Added Ubuntu and PCLinuxOS sections to download page.