Fix double dash

[schoettl]

This fixes this problems:

• discard -- from arguments to add command

It does not fix the that -5 gets translated --depth 5 even after --.

[schoettl]

• run hledger tests locally
• just functest – 5 failed test cases on NixOS, same on master
• how about other commands?

I think the problem that double dash is passed as arg to some commands is hard to fix globally because the args are taken within the command's function (e.g. within add :: CliOpts -> Journal -> IO () here).

[schoettl]

It does not fix the that -5 gets translated --depth 5 even after --.

Looks like this isn't a problem at all:

$ hledger bal assets: -- -1
          123 €  assets:bank:yyy
          456 €  assets:prepaid:gifts
--------------------
          123456 €  

So in this example, -1 isn't interpreted as option because it's after a double dash. Hence it isn't converted to --depth 1.

But the balance command as well misinterprets the double dash. It should be discarded there, too.