Builtins not at the end of a pipeline are executed in the main shell process

[Raphael-Mabille]

Example

cd | pwd cd isn't executed in a child process and thus change to working directory of the shell.

Expected result

$> _pwd_
/home/user/directory
$> _cd | pwd_
/home/user/directory
$>

Actual result

$> _pwd_
/home/user/directory
$> _cd | pwd_
$> /home/user/directory
_pwd_
/home/user
$>

Text between underscores is user input.

[ThibautHH]

Fixing in #20.