patch, 5 partsAdd easy access to SVN properties in git-svn.

Hello, this is a fairly simple patch series that adds easy access to SVN properties from within git-svn.

The first patch simply factors some code that was used for git-svn show-ignore in order to easily implement git-svn create-ignore (2nd patch). The 3rd and 4th patch implement git-svn propget / proplist to easily access SVN properties. The last patch does some cleanup because I found it more convenient to not have to remember to add a `\n' at the end of each error message.

 git-svn.perl             |  201 +++++++++++++++++++++++++++++++++++++---------
 t/t9101-git-svn-props.sh |   72 ++++++++++++++++-
 2 files changed, 233 insertions(+), 40 deletions(-)