Calls to svnkit.http.methods are only made in "SubversionSCM.java" from what I can tell.
The editor made no notes as to why they would have changed a call like:
System.setProperty("svnkit.http.methods","Digest,Basic,NTLM,Negotiate"); // as it was in 2.4.5
System.setProperty("lib.svnkit.http.methods","Digest,Basic,NTLM,Negotiate");// as it is now in 2.5
Maybe someone can find the reason in the check-in that changed the file.
Changing all calls to "lib.svnkit.http.methods" back to "svnkit.http.methods" in this file and recompiling the* .hpi *image seems to allow me to check out my repositories without issues.