svn:externals repository named "http" or "https" and USE_SSH=yes

When using "USE_SSH=yes" and having a svn:externals repository named "https" (for example), the bash substitution pattern for "svn+ssh" is replacing all matches with "svn+ssh".

say:
**https**://svn.repo.srv/svn/**https**/trunk
will be substitute with
**svn+ssh**://svn.repo.srv/svn/**svn+ssh**/trunk
