Update URL in SampleUsage.java
URL links to images on GitHub, not Google Code.
Better JPEG specification conformance.

The spec (now added to the wiki's docs folder) explains in section B.1.1.2
that there may be many additional 0xFF bytes before a JPEG segment marker
byte. This patch extends upon earlier work by Ricardo in issue #29, and
offers a more general solution.
Suppress warning about ignorable off-by-one error in IPTC data length.