Gnuplot treatment of temporary files

[Jari Häkkinen]

In Gnuplot.h there is a template function that uses mkstemp to acquire unique filenames. If succesful mkstemp return a file descriptor to a file opened for writing. This should be used to initialize a output stream. As it is now, a stream is created using the unique file name ..... the file is opened twice! And consequently closed twice. Previouisly the file was closed only once leading to too many opened files error. Fix the code to use the mkstemp file descriptor.

[Jari Häkkinen]

Removed temporary file usage completely. Now using gnuplot's ability to receive inline data in commands.