subversion: update to 1.7.10; build without neon, use serf; remove ENV.d...

...eparallelize because it did not fix #13226

On my test machine, issue #13226 does not occur anymore, after this commit. ENV.deparallelize was definitely not necessary (many still experienced the problem with it), that's why I removed it.

I hope somebody can verify that #13226 also does not occur anymore on his or her machine?

Regards, Clemens