add output file redirection
set initial PATH to bin/
modify initial PATH setting and printenv command output
add TA testing file in TA_test dir, replace commands/ dir

using make TA_test to build testing environment of ras shell.
bug fix of stderr output to client. add 2nd type of welcome msg in comment mode.

stderr output fix
1. remove close() after dup2() for simple fd dup to multiple target.
2. add error message for execvp() failed.
update gitignore for TA_test
add failed process checking, which doesn't drive number pipe.