Hi

I found a bug in the ClassicPluginStrategy. When the .timestamp file is created
the lastModifiedTime is set to the machine current time, which is then compared
to the HPI file lastModifiedTime and if the latter is greater then the plugin is
re-extracted and updated. However the HPI lastModificationTime of the
pre-installed plugin(s) is set to the date when the plugin was compiled and for
that reason the plugin is never updated (current machine time is always greated
than the compilation time).

The bug can be reproduced by using following steps:
1) install and start new hudson 1.320
2) check the plugin version of
<HUDSON_HOME>/plugins/maven-plugin/META-INF/MANIFEST.MF
3) stop hudson, update it to version 1.321, and start it again
4) check the plugin version again. It is still 1.320

I narrow down the problem inside the ClassicPluginStrategy, so instead of using
the machine current time it is setting the .timestamp lastModifiedTime to HPI
file lastModifiedTime.

Best regards
Kiril