stddoclet: Add -packagesheader to standard.properties

The -packagesheader was added in 1.4.2 but not documented, due to
compatibility concerns of someone wanting to use it in 1.4.1.
This option needs to be added to standard.properties and documented
in the documentation for 1.5.0.
###@###.###

Can wait til 1.6.0, as this option was requested only internally.
###@###.### 2003-09-24