Fixed a bug where an xterm window was launching even if an X session was...

The code was launching an xterm window in spite of an already present X Session. The check was against the variable `$isxrunning`, and it looks like the conditions were inverted. If the variable was null, screen was used, and if the variable was not null, xterm was used.

That code has been replaced by $isrunning -eq 1 to check whether the variable has been set to 1 in the `f_isxrunning()` function.

Thanks to  <a href='https://github.com/connection/'>connection</a> for help with these fixes.