TPS PencilBeam source crashes on old source properties files

[djboersma]

A recent update to the TPSPencilBeam source changed the parsing of the source properties files, it is now expecting to find the beam monitor calibration N/MU at the end. If this information is missing (like in all source properties files that were used prior to this fix), then Gate crashes with an error that does not make it clear what is missing. Suggested solutions:

1. If the beam monitor calibration is missing, then we give an error message describing this problem and a suggestion for the fix, and then Gate exits (with an error value).
2. If the beam monitor calibration is missing, then we assume default values for it, basically assuming N/MU=1. A WARNING is printed twice, namely once immediately after parsing the source properties file and once at the end of the run.

My own preference would be (2). In addition to fixing the TPSPencilBeam code, we should update the source properties files in GateContrib. (The ones in GATE-RTion seem to fine, but three others in the dosimetry and imaging section are currently not compliant to the new standard and will result in the above mentioned error.)

[djboersma]

Option (2) will help to keep Gate backward compatible: Gate macros that work with older releases should preferably also work with newer releases. But if we really want that, then we should also use the old hardcoded N/MU calibration, which was definitely not N/MU=1.