astFreeastFree - Free previously allocated memory

Description:
This function frees memory that has previouly been dynamically allocated using one of the AST memory function.
Synopsis:
void $*$astFree( void $*$ptr )
Parameters:
ptr
Pointer to previously allocated memory. An error will result if the memory has not previously been allocated by another function in this module. However, a NULL pointer value is accepted (without error) as indicating that no memory has yet been allocated, so that no action is required.
Returned Value:
astFree()
Always returns a NULL pointer.