Support for curl as alternative to wget, various other improvements

* Added support for using curl as alternative to wget (set REQTOOL in script or enable by specifying "-c" on the command line.)
* Move all "User settings" to the beginning of file
* Check existence of needed cert/key files
* Check some intermediate processing files to be not empty
* Show detail text on failures beside MSS code
Only roughly tested.

Fixes #3 and #6