cliinterface: Use KPtyProcess on non-Windows platforms.

Once again inspired by Okular's comicbook generator (and also by Ark's
code circa the 4.2 release, which also seems to have borrowed the same
ideas from Okular), we now use a KPtyProcess on non-Windows platforms.

Some programs (such as unrar) open a TTY in occasions such as showing
password prompts, as they usually use getpass(3).

This is the first step towards supporting header-protected rar and 7z
files.

svn path=/trunk/KDE/kdeutils/ark/; revision=1216558