[JENKINS-16215] Avoiding unnecessary downloads in FilePath.installIfNecessaryFrom.

The updated version uses the locally cached timestamp, '.timestamp', to set the
'If-Modified-Since' header. 304 Not Modified responses are dealt with by
aborting the installation.
German translation for GlobalProjectNamingStrategyConfiguration
clarified English help

The help message was uninformative about the impact of this setting on
job execution.
[maven-release-plugin] prepare release jenkins-1.496
[maven-release-plugin] prepare for next development iteration
updated changelog for release
updated changelog as a part of the release
merged back the RC branch
creating an RC branch
the trunk is toward 1.498-SNAPSHOT
Merge pull request #661 from albers/translation

German translation for "Restrict project naming" feature
doc improvement
Added a new tag to create the bottom sticking button bar.
bumped up various library dependencies
Using <f:bottomButtonBar> in more places.

Plus fixing the wrong apply button handling in various code.
adding the default constructor
exposing this code to outside
making my old  compiler happy
making compiler happy cont'd
making compiler happy cont'd