Clarify JarInputStream Manifest access

A DESCRIPTION OF THE PROBLEM :
If MANIFTEST.MF is not the first (or second) entry in a .jar-file, JarFileInputStream does not find the MANIFEST.MF.

It should be better documented (in JavaDoc-comment), that it checks only the first (two) entries so that the result of null of getManifest()-method does not explicit mean, that there is not any MANIFEST.MF.

As for a RFE the class could offer a convenience setting, that it checks for that on every call to getNextEntry() and when found, populate the internal Manifest-variable so that after all entries were scanned, getManifest()'s result really shows if there is or is not an MANIFEST.MF in the jar.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
create a .jar, where the MANIFEST.MF is not one of the first two entries (any normal Zip-Programm could do that)


FREQUENCY : always