Updated OME-XML schema paths

These paths were still pointing to loci/formats packages. Thus, if the
scifio.jar was present they would be found - but not if scifio-devel was alone
on the classpath.
Removed currentId check from optimal tile methods

CurrentId doesn't reflect whether or not metadata is attached, and thus
is an unnecessary check before getting OptimalTileWidth/height.
Merge branch 'omexml-fixes'

Corrected path to OME-XML schema, and fixed optimalTileWidth/Height methods in
OME-TIFF format.