VarRename

  VarRename overwrites a variable name in a Level 5 Version 6 MAT-File
  or returns the number of bytes reserved for the name.

  Example:
  BYTES=VARRENAME('MYFILE','MICKY')
  returns the number of bytes available for the name of the existing
  variable 'MICKY'

  FLAG=VARRENAME('MYFILE','MICKY','MICKEY')
  replaces the existing name with the new name if there is space.
  Returns 0 if the rename has taken place, -1 otherwise

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  This program is distributed without any warranty,
  without even the implied warranty of fitness for a particular purpose.
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  Author: Malcolm Lidierth 11/06
  Copyright © The Author & King's College London 2006
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