Remove offset mapping limit.

For some reason, which never was found, this causes artifacts at the
fragments right at the border. However, since the offset enabled
material only is used on near pages there's no major performance hit
removing this check.
Fix incorrect names.
Specify all used parameters up front.

Those not used will be culled by the compiler. This at least works on my
setup, and fixes an issue with log error messages when the parameters
defined in the .program can't be found.
This might however need more testing to find whether there are any
issues.