Fix spelling error in svnadmin message and make gettext-friendly

* subversion/svnadmin/svnadmin.c
  (sub_main): fix spelling, fix macro call breaking gettext

Approved by: danielsh


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1435190 13f79535-47bb-0310-9956-ffa450edef68