If you get
checking for svn includes... configure: error: failed to find svn_client.h
Try
sudo apt-get install libsvn-dev
The Subversion binaries are not necessary to use this extension. However, when compiling the extension, libsvn (the Subversion headers) must be available.
If you get
checking for svn includes... configure: error: failed to find svn_client.h
Try
sudo apt-get install libsvn-dev