Amalgamate two strings to form the return value
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 Syntax

        GT_CharMix(<cStr1>, <cStr2>) --> cRet

 Arguments:

      <cStr1>  - A character string to mix
      <cStr2>  - A character string to mix with

 Returns:

      cRet     - A string consisting of all the characters in <cStr1>
                 mixed with all the characters in <cStr2>

 Description:

      Return a string consisting of all the characters in <cStr1>
      mixed with the characters from <cStr2>.

      NOTE:
         invalid parameters will return ""

 Examples:


      ? gt_CharMix("abc", "123")               // prints "a1b2c3"
      ? gt_CharMix("abcde", "123")             // prints "a1b2c3de"
      ? gt_CharMix("abc", "12345")             // prints "a1b2c345"


 Source: CHARMIX.C

 Author:  Andy M Leighton