fix syntax of equality test in /bin/sh

[walterdejong]

Teus Hagen wrote me an e-mail saying:

The script shield-trigger-iptables is using the sh (an falls down in some distros like Debian into the dash) engine.
In dump sh the test function will fail on arguments starting with the '-' symbol.
Maybe change "#! /bin/sh" to "#!/bin/bash" ?

To test it:
sh -c "[ -D == -D ]"

The failure message:

/usr/sbin/shield-trigger-iptables: 37: [: -D: unexpected operator
/usr/sbin/shield-trigger-iptables: 45: [: -D: unexpected operator
iptables v1.4.18: Couldn't load target `pam_shield':No such file or directory

The fix is to use a single = rather than == since this is for /bin/sh.

Greets,

--Walter

[drydenp]

I can confirm that this patch would be necessary for Dash to function properly.