capture difference between symbols and alias symbols

[graybeal]

It's doubtful that the difference between symbols and alias symbols carries much importance in UDUNITS. Mostly this seems to reflect whether the symbol is for an alias or for a name; but in at least one place it looks like the alias symbol is just less important. (Or, maybe the alias originally existed but was deprecated, and the symbol remains.)

A fully faithful rendition of the vocabulary should capture this distinction (e.g., by giving the alias symbols a hasRole "alias" property).

I'd call this pretty low priority.

[carueda]

Example?