Add a 5 minute connection timeout to ssh slave launch() function.

Some improvements to ssh slave launch logging.
Remove untranslated messages from properties files.
Add configuration option to set the ssh launch timeout in seconds.

Leaving it blank or setting it to 0 will disable timeouts.
Merge pull request #15 from christ66/master

Upgrade default jdk install from jdk-6u16 to jdk-6u45 because jdk6u16 is outdated.
Update credentials plugin to 1.9.4
Update ssh-credentials plugin to 1.6
No need for the "add some" link now  that we depend on credentials 1.9.4
Update ssh-credentials plugin to 1.6.1
Merge branch 'connect_timeout' of github.com:pure-marcmac/ssh-slaves-plugin

Also tidy-up of the code being merged

Conflicts:
	src/main/java/hudson/plugins/sshslaves/SSHConnector.java
	src/main/java/hudson/plugins/sshslaves/SSHLauncher.java
[maven-release-plugin] prepare release ssh-slaves-1.6
[maven-release-plugin] prepare for next development iteration
Protect against the case where there is no private key, which results
in a NPE when trying to compare in pemKeyEquals. This seems to happen
particularly when the plugin has been upgraded, and it's trying to find
existing key matches for keys with a username/password, but no private
key.

This is possibly the root cause of JENKINS-20332.


Signed-off-by: Nigel Magnay <nigel.magnay@gmail.com>
added help items
localization cleanup
updated German localization
wrong constructor invoked (thanks to untyped null values)
attempting to improve error diagnostics
no need to fully qualify "java.lang"