bash: update 'git svn' options

bash: update 'git svn' options

'git svn' got some new subcommands and otions in the last couple of
months.  This patch adds completion support for them.

In particular:

  * 'fetch', 'clone', etc.: '--ignore-paths='
  * 'init' and 'clone': '--prefix=', '--use-log-author',
                        '--add-author-from'
  * 'dcommit': '--commit-url', '--revision'
  * 'log': '--color'
  * 'rebase': '--dry-run'
  * 'branch', 'tag', 'blame', 'migrate' subcommands and their options

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Acked-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>