The importdata function returns empty lines on R2014a, while it omits them in
R2020a. Moreover, importdata is not meant to parse arbitrary text file. We thus
replace it by repeated calls to fgetl.

unique(…, 'stable') does not exist in Octave 5.

The blockname tag was overwritten (with the name of the LHS endogenous variable).

... Or has special characters. In this cases we use the LHS variable
as a name for the equation.

aggregate was crashing in the absence of tags on the endogenous or exogenous variables.