Option sort in usage help should ignore prefix

[remkop]

Currently, options that only have a long name (and do not have a short name) are always shown before options with a short name. For example:

Usage: git commit [--squash=<commit>] [-m=<arg0>] [<file>...]
      [<file>...]
      --squash=<commit>
  -m, --message=<arg0>

Instead, they should be inserted in the list by their first non-prefix letter.

Should be:

Usage: git commit [-m=<arg0>] [--squash=<commit>] [<file>...]
      [<file>...]
  -m, --message=<arg0>
      --squash=<commit>