In a multitask environnment, applications are launched in parallel. With the parameter single, applications are lauched in single mode. If the parameter av is set to TRUE, a VA_START message is sent to the GEM application if it is running. Otherwise, a FALSE value has the consequent to create multiple application.
The parameter cmd describe the command line given to the application. The format is different of Pexec() or shel_write() (ie the first character does not contain the lenght of the string).
This function was backwardly nammed 'ExecGemApp()'.