[Rd] libxml2.2.dylib compatibility problem opening browser (PR#7063)

[theodos at csd.auth.gr]

Full_Name: Theodosios Theodosiou
Version: 1.9.1
OS: MAC OS X (10.3.4)
Submission from: (NULL) (193.62.199.161)


dyld: /usr/bin/open version mismatch for library: /usr/local/lib/libxml2.2.dylib
(compatibility version of user: 9.0.0 greater than library's version: 8.0.0)

type help.start() to reproduce the problem. Have checked the "Show system error
output in R console of the Misc tab at Preferences".