add_variable.php and edit_var.php: sort the drop-downs alphabetically

jirikadlec2[CodePlex]
The drop-downs quotVariable Unit Type:quot and quotUnit:quot in add_variable.php and edit_var.php are not sorted from A-Z. As a result it's difficult to find the unit type and the unit name in the drop-down.

Suggestion:
Sort the Variable Unit Type and Unit drop-downs alphabetically (same as all the other drop-downs).

Open add_variable.php and edit_var.php and locate the Variable Unit Type and Unit drop-downs. Compare them with the other alphabetically sorted drop-downs, then verify that both requested lists display in A–Z order.

Written by the indexing model from the issue text.