GetExtension: Determine the extension part of a filename
Ext=GetExtension(FileName)
Return the last part of the filenanem starting from the character that
follows the last dot in the FileName.
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Parameters
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FileName - a string that may or maynot contain the full path
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Returned values
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Ext - the last part of the filenanem starting from the character that
follows the last dot in the FileName.
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Remarks
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Zsolt Csaba Johanyák, johanyak.csaba@gamf.kefo.hu, v. 1.0, 10. November 2006.