Run the code-signing script from the target dir

[manics]

Fix a build problem introduced in #2193. Enter target/ before running the code-signing script, so that temporary and log files will be removed by ./build.py clean. Also disable webstart signing in the update-version target.

Testing: check webstart works, check gretzky webstart is self-signed, check RELEASE builds aren't signed. Also look out for any instances of unwanted signing if you want, I've got a verification summary script at https://github.com/manics/certificate-generation/blob/master/omero/verify_jars.py

[manics]

--rebased-to #2238

[manics]

One more pending change suggested by @kennethgillen ... check system proxy env vars and convert them to whatever Java wants when timestamping.

[joshmoore]

From http://ci.openmicroscopy.org/job/OMERO-5.0-merge-ice33/203/consoleFull

++ '[' -z '' ']'
++ pushd target
/opt/hudson/workspace/OMERO-5.0-merge-ice33/src/target /opt/hudson/workspace/OMERO-5.0-merge-ice33/src
++ ../docs/hudson/omero_insight_sign.py ../lib/keystore omedev OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203.zip -kp omedev -cp omedev -ts no -oz OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203.zip
2014-04-03 06:15:16 Unzipping OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203.zip
2014-04-03 06:15:22 Signing OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203/lib/insight/specification.jar
2014-04-03 06:15:24 Signed OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203/lib/insight/specification.jar
...
2014-04-03 06:17:23 Renaming OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203.zip to OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203.zip.bak
2014-04-03 06:17:23 Zipping OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203.zip
2014-04-03 06:17:47 Creating OMERO.server-5.0.1-rc1-155-d1d79c1-ice33-b203.zip.md5
++ popd

Certainly looks good. Will discuss with @kennethgillen, but likely this will need to be merged for testing with 5.0.1

[manics]

--rebased-to #2321