I've gotten this to work with another project just before but it's absolutely refusing to do it now and I'm not sure as to why. Here is what I'm doing:
svn checkout https://github.com/WordPress/WordPress/branches/3.9-branch .
then...
svn update —set-depth=exclude wp-content
rm -fr wp-content
lastly...
svn propset svn:externals “wp-content” http://svn.example.com.au/site/ wp-content/
Every time I try and run svn externals it continuely keeps saying the following:
svn: E200009: Cannot mix repository and working copy targets
Which makes zero sense because I have done the exact same with another project just before and it didn't give me no such errors.
I'm going out of my mind.
Thank you very much for anyones help!