added a new routine xmlBuildRelativeURI needed for enhancement of

* uri.c, include/libxml/uri.h: added a new routine
  xmlBuildRelativeURI needed for enhancement of xinclude.c
* xinclude.c: changed handling of xml:base (bug 135864)
* result/XInclude/*: results of 5 tests changed as a result
  of the above change
9 files changed