The builtin_cmd function returns 1 to eval if the command was one of the "builtin" commands and 0 otherwise.

For a return value of 1, eval should just return to main for the next command.

If the command was not built-in, however, eval must work!

Part of the work is:

• create a child process
• the child process uses the array result of parseline to execute the command.
• the parent (the shell), waits for the child or not depending on whether the command line ended with an ampersand &