Replace StringBuffer usages with StringBuilder

[dustinkredmond]

For better thread safety going forward. Replace usage of StringBuffer with StringBuilder.

Also, while working in TarEntry.java I took the liberty of fixing the danling javadoc comment, switched to the more modern enhanced for loop where applicable and changed the below for loop to a while loop for better readability.

• for (; offset < outbuf.length;)

• while (offset < outbuf.length)