Bug 47423

just sharing with the community, an extra attribute we find useful for the core task tstamp in org.apache.tools.ant.taskdefs.TStamp.java

one of the things we often have to do is to schedule a task that has to work with the output saved in files which are named as their timestamp with granularity 15 minutes.  e.g.: 20090625T101500

we want to name our files so that they are "close" to the input files and we decided to use the original timestamp, offset by one or more minutes.  e.g.: 20090625T101600 20090625T101700 etc.

for this we use the granularity attribute described in #45089 and a similar offset attribute, whose implementation is just as trivial.