more build dependencies fixes

We do depend on libsoup-2.4 after all: the API and ABI
changed considerably between 2.2->2.4.

Building D-Bus service depends on xsltproc. Added
to README and added an AC_ERROR in configure, to avoid
compile errors later on.

README

@@ -685,7 +685,7 @@ files. For HTTP, either Curl or libsoup can be used.
 On Debian based systems the required packages can be installed with
    apt-get install evolution-data-server-dev \
                    libecal1.2-dev libebook1.2-dev \
-                   libsoup2.2-dev \
+                   libsoup2.4-dev \
                    libboost-dev
 
 libboost-dev >= 1.34, available as libboost1.35-dev backport for Debian Etch.
@@ -703,6 +703,7 @@ The test framework also requires CPPUnit:
 
 For the GUI and its D-Bus based service backend:
    apt-get install libdbus-glib-1-dev \
+                   xsltproc \
                    libglib2.0-dev \
                    libgtk2.0-dev libglade2-dev \
                    libgnome-keyring-dev \

configure-pre.in

@@ -258,6 +258,9 @@ if test $enable_dbus_service == "yes"; then
     PKG_CHECK_MODULES(DBUS_GLIB, dbus-glib-1 glib-2.0)
     AC_PATH_PROG(DBUS_BINDING_TOOL, dbus-binding-tool)
     AC_PATH_PROG(GLIB_GENMARSHAL, glib-genmarshal)
+    if test -z "$XSLT"; then
+       AC_ERROR([xsltproc not found, is required for D-Bus service])
+    fi
 fi
 AC_SUBST(DBUS_GLIB_CFLAGS)
 AC_SUBST(DBUS_GLIB_LIBS)