#437 Allow predefined keywords as Identifiers

[Rainer Müller]

The parser treats currently predefined keywords like (A,F,E,...) different from names of identifiers.
This behavior should be changed that the following code fragment becomes valid

DCL F FIXED;
...
PUT F TO stdout BY F(3),SKIP;

In a first step the format and position elements should by treated

The correct treatment of names of operators (CSHIFT, EXP,...) will be more sophisticated.