Set permissions attribute in Ant; add sign target.

We now have a code signing certificate, so the installer jar should be
signed.
Remove permissions attribute update from build-all

The Ant build script does it now, which is more appropriate.
Sign jar in build script.
Fix update.sh when called from other directories
Fix keystore path; allow giving keypass

Environment variables are not substituted in value strings, but
environment variables can be accessed. Giving the keypass allows using
a keypass different from the storepass.
Set jarsigner attributes from environment variables

The build scripts work from a fresh clone of the repo, so for easier use
with them the default jarsignier configuration comes from environment
variables.
Disable strict jarsigner

The sun java6 package does not support it. It'd be reasonable to enable
it (as it certainly should be) along with the move to Java 7. This way
the build verification setup can be changed one time instead of twice.