model.xml may be saved in a non-validating state

[sebjameswml]

If you have a population with a state variable property, and you leave the state variable initial value un-set, (that is you don't choose FixedValue, Random or List) then the model.xml is saved with a property that looks like this:

<Property name="a" dimension="?"/>

which fails validation. This will become an issue after I've pushed the new xmllinting code in SpineML_2_BRAHMS/convert_script_s2b. Flag @mondus @ajc158

[mondus]

Alex, didn't you fix this in one of your branches so that they would be given a default fixed value of 0 when saved?