sort flags with the same name in a consistent order

before:
```
: trevize docker master ; docker --help 2>&1 | fgrep -i -- '-g'
  -g, --graph="/var/lib/docker"             Path to use as the root of the docker runtime
  -G, --group="docker"                      Group to assign the unix socket specified by -H when running in daemon mode
: trevize docker master ; docker --help 2>&1 | fgrep -i -- '-g'
  -G, --group="docker"                      Group to assign the unix socket specified by -H when running in daemon mode
  -g, --graph="/var/lib/docker"             Path to use as the root of the docker runtime
: trevize docker master ; docker --help 2>&1 | fgrep -i -- '-g'
  -G, --group="docker"                      Group to assign the unix socket specified by -H when running in daemon mode
  -g, --graph="/var/lib/docker"             Path to use as the root of the docker runtime
```

after:
```
: trevize docker master ;  bundles/0.11.1-dev/binary/docker --help 2>&1 | fgrep -i -- '-g'
  -G, --group="docker"                      Group to assign the unix socket specified by -H when running in daemon mode
  -g, --graph="/var/lib/docker"             Path to use as the root of the docker runtime
: trevize docker master ;  bundles/0.11.1-dev/binary/docker --help 2>&1 | fgrep -i -- '-g'
  -G, --group="docker"                      Group to assign the unix socket specified by -H when running in daemon mode
  -g, --graph="/var/lib/docker"             Path to use as the root of the docker runtime
: trevize docker master ;  bundles/0.11.1-dev/binary/docker --help 2>&1 | fgrep -i -- '-g'
  -G, --group="docker"                      Group to assign the unix socket specified by -H when running in daemon mode
  -g, --graph="/var/lib/docker"             Path to use as the root of the docker runtime

```