Replace FILE-LOADED with ERROR-CODE and ERROR-TEXT
Created by: Lartu
Right now, LDPL has one control variable, FILE-LOADED, that's used by the language to tell whether a file has been loaded right or not. That's a little specific, as many other statements could also benefit from having a control variable to check if they executed correctly or not. This variable should be replaced with two other variables, ERROR-CODE, that should store an error number regarding the result of the operation, and ERROR-TEXT that should store a human readable report of what went wrong (or not).
FILE-LOADED is declared here and used here. At the moment no other function than LOAD FILE uses it, but WRITE TO, APPEND TO, numeric ACCEPT and type conversions should use it as well.