Ease your vendor branch management worries with Piston, a tool to copy vendor / upstream code to your own repository, while preserving your local patches.
Use the convert subcommand if you have a Subversion working copy in which you have svn:externals references. This command will convert each of the svn:externals references running import on each of them.
SYNOPSIS piston convert [directories*] [options]+ PARAMETERS directories (-1 ~> directories) Which directory/directories to convert from svn:externals to Piston. Not specifying this argument recursively converts the whole directory tree starting from the current dir. --verbose=[verbose], -v (0 ~> integer(verbose=0)) Verbosity level (0 to 5, 0 being the default) --quiet, -q --force --dry-run --help, -h