CKSLEN    CKSLEN    CKSLEN    CKSLEN    CKSLEN    CKSLEN    CKSLEN    
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                              ******

INTEGER FUNCTION CKSLEN (LINE)
Returns the effective length of a character string, that is,
the index of the last character before an exclamation mark (!)
indicating a comment.

INPUT
LINE     - Character string.

OUTPUT
CKSLEN   - Integer scalar, the effective length of LINE.