Subversion --Perl

Patch suggested by @pwagland that should finally fix the --perl binding mv issue that causes the entire formula to error out if --perl build option is invoked. The issue & consequent patch will not affect anyone who doesn't build subversion with perl.

I've included a # explanation as to why the change has been made, as hopefully this patch can be replaced either by a subversion fix or a better Ruby-invoked fix in time. Although this could work as a permanent fix, the hope is that it's a temporary workaround until something cleaner is worked out.

See the following issues for more detail:

[1](https://github.com/Homebrew/homebrew/issues/30370)
[2](https://github.com/Homebrew/homebrew/issues/30224)
@mikemcquaid This doesn't appear to work. When I make that change, the installation still fails, with the following error:

```
$ brew install subversion --perl
==> Downloading http://www.apache.org/dyn/closer.cgi?path=subversion/subversion-1.8.9.tar.bz2
Already downloaded: /Library/Caches/Homebrew/subversion-1.8.9.tar.bz2
==> Patching
patching file subversion/bindings/swig/perl/native/Makefile.PL.in
Hunk #1 succeeded at 76 (offset 7 lines).
patching file configure.ac
==> Downloading https://serf.googlecode.com/svn/src_releases/serf-1.3.6.tar.bz2
Already downloaded: /Library/Caches/Homebrew/subversion--serf-1.3.6.tar.bz2
==> /usr/local/opt/scons/bin/scons PREFIX=/usr/local/Cellar/subversion/1.8.9/libexec/serf GSSAPI=/usr CC=/usr/bin/clang CFLAGS=-Os -w -pipe  -march=native -mmacosx-version-min=10.9 LINKFLAGS=-L/usr/local/opt/openssl/lib -L/usr/local/opt/sqlite/lib -L/usr/local/opt/readline/lib -L/usr/local/lib -F/usr/local/Frameworks
==> /usr/local/opt/scons/bin/scons install
==> ./autogen.sh
==> ./configure --prefix=/usr/local/Cellar/subversion/1.8.9 --with-apr=/usr/bin --with-zlib=/usr --with-sqlite=/usr/local/opt/sqlite --with-serf=/usr/local/Cellar/subversion/1.8.9/libexec/serf --disable-mod-activation --disable-nls --without-apache-libexecdir --without-berkeley-db
==> make
==> make install
==> make tools
==> make install-tools
==> make swig-pl
==> make install-swig-pl DESTDIR=/usr/local/Cellar/subversion/1.8.9
Error: same file: /usr/local/Cellar/subversion/1.8.9/lib/libsvn_client-1.0.dylib and /usr/local/Cellar/subversion/1.8.9/lib/libsvn_client-1.0.dylib
Please report this bug:
    https://github.com/Homebrew/homebrew/wiki/troubleshooting
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/fileutils.rb:1551:in `block in fu_each_src_dest'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/fileutils.rb:1566:in `fu_each_src_dest0'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/fileutils.rb:1550:in `fu_each_src_dest'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/fileutils.rb:508:in `mv'
/usr/local/Library/Homebrew/extend/pathname.rb:64:in `install_p'
/usr/local/Library/Homebrew/extend/pathname.rb:24:in `block (2 levels) in install'
/usr/local/Library/Homebrew/extend/pathname.rb:24:in `each'
/usr/local/Library/Homebrew/extend/pathname.rb:24:in `block in install'
/usr/local/Library/Homebrew/extend/pathname.rb:13:in `each'
/usr/local/Library/Homebrew/extend/pathname.rb:13:in `install'
/usr/local/Library/Formula/subversion.rb:176:in `install'
/usr/local/Library/Homebrew/build.rb:172:in `block in install'
/usr/local/Library/Homebrew/formula.rb:259:in `block in brew'
/usr/local/Library/Homebrew/formula.rb:564:in `block in stage'
/usr/local/Library/Homebrew/resource.rb:62:in `block in unpack'
/usr/local/Library/Homebrew/extend/fileutils.rb:21:in `mktemp'
/usr/local/Library/Homebrew/resource.rb:59:in `unpack'
/usr/local/Library/Homebrew/resource.rb:52:in `stage'
/usr/local/Library/Homebrew/formula.rb:562:in `stage'
/usr/local/Library/Homebrew/formula.rb:254:in `brew'
/usr/local/Library/Homebrew/build.rb:149:in `install'
/usr/local/Library/Homebrew/build.rb:44:in `main'
/usr/local/Library/Homebrew/build.rb:10:in `block in <top (required)>'
```