Since previous commit dafe51e8

,
the gtk-doc is no longer ignored. However, the angle brackets
add invalid XML characters to ./docs/libnm-glib/xml/nm-client.xml
This breaks the build.

    make[3]: Entering directory `./NetworkManager/docs/libnm-glib'
      DOC   Scanning header files
      DOC   Introspecting gobjects
      DOC   Building HTML
    ../xml/nm-client.xml:1110: parser error : Opening and ending tag mismatch: NMActiveConnection line 1109 and para
    </para></refsect2>
           ^
    ../xml/nm-client.xml:1110: parser error : Opening and ending tag mismatch: para line 1107 and refsect2
    </para></refsect2>
                      ^
    ../xml/nm-client.xml:1211: parser error : Opening and ending tag mismatch: refsect2 line 1104 and refsect1
    </refsect1>
               ^
    ../xml/nm-client.xml:1262: parser error : Opening and ending tag mismatch: refsect1 line 1095 and refentry
    </refentry>
               ^
    ../xml/nm-client.xml:1263: parser error : Premature end of data in tag refentry line 7

    ^
    ../libnm-glib-docs.xml:67: element include: XInclude error : could not load ../xml/nm-client.xml, and no fallback was found
    make[3]: *** [html-build.stamp] Error 6

Signed-off-by: Thomas Haller <thaller@redhat.com>