eliminate misleading flag parsing error

[rade]

The standard mflags error reporting produces an error like

flag provided but not defined: -p
See '/home/weave/weaver --help'.

on stderr. This is misleading since the program name is container local, so not something the user actually invoked. Furthermore, what the user can invoke doesn't have a --help option.

With this change the error becomes

FATA: 2015/08/18 10:56:23.635119 Incorrect usage: flag provided but not defined: -p

There are a few issues with this:

• we no longer get a usage message
• we no longer get deprecation warnings logged

Fixes #1321. Alas I am not at all happy with this. Wasted several hours on this already. Somebody else please have a go.

[awh]

vagrant@vagrant-ubuntu-vivid-64:~/weave$ ./weave launch -p
The weave container has died. Consult the logs with 'docker logs weave' for further details.
vagrant@vagrant-ubuntu-vivid-64:~/weave$ docker logs weave
flag provided but not defined: -p
See 'weave help'.

Feel free to squash if you're happy with the approach

[rade]

@awh see what you make of this one. I've left the old commits in and reverted them, just in case we change our mind once more. If not, I'll squash them away.

[awh]

That seems entirely reasonable to me, given the lack of flags support for overriding the executable name in sane fashion...

[awh]

The only other option appears to be vendoring mflags, which strikes me as wholly unappealing 😒