fix servlet classpath clash

The servlet API jar files are signed.  Recent versions of java (or
possibly bug http://bugs.sun.com/view_bug.do?bug_id=6805618 ) means
that, on some platforms, all the classes in a package must be signed
by the same certificate.  A failure results in an error message and
dCache failing to startup.

Currently, dCache includes a Jetty-supplied 'javax.servlet' jar file
(v3.0), and a 'javax.servlet'-supplied 'servlet-api' jar file (v2.5).
These are signed by different certificates and, since the v3.0 file
contains additional classes, if v2.5 precedes v3.0 in the classpath
then the classloader will find classes in the same package with
different signatures.

The previous version of Jetty depended on servlet-api jar file and,
while this too had two jar files (a Jetty-supplied and a
'javax.servlet'-supplied) since the two jar files have the same set of
classes, the classloader will take javax.servlet.* classes from one
jar file, independent of classpath order.

This patch fixes this problem by excluding the references to
servlet-api dependency in axis and axisg jar files.

Target: master
Requires-nodes: no
Requires-book: no
Patch: http://rb.dcache.org/r/5757
Acked-by: Gerd Behrmann