COMP: Fix segfault in vtkWrapJava on underscores in method names.

On OS X 10.5, PowerPC, it was reported that vtkWrapJava crashed
on some input files, and a stack trace identified a strncat call
in part of the code that is meant to handle method names that
contain underscores.  I could not reproduce the problem on my
system (not even by adding asserts to guard against overflows),
so I have re-written the code to eliminate strcat and strchr.

Backport of 4ee34ca5 from master to release.

Change-Id: I50d7b861b86ab185eae9b5acd5b9644cabb7bcf5