projman #229593 improve error message [validation pending]

display task name instead of task number:

task[0]/task[7]/constraint-task[1]:attribute idref is missing

is now displayed as:

task[project]/task[q3]/constraint-task[1]:attribute idref is missing
prioritynormal
typeenhancement
done in0.16.1
load0.100
load left0.000
closed by#1a74ce397fef [checker] improve a bit the displayed errors (closes #229593)
patch[checker] improve a bit the displayed errors (closes #229593) [applied]