Replace deprecated Date.toGMTString() with DateFormat
Move testPurgeTempDir to be with other HoyaFileSystem tests
Replace deprecated FileSystem.getLength with getFileStatus
Remove deprecated junit.framework.Assert
Eliminate raw types
Remove unused imports

Remove unused imports and imports used only in links within javadoc.
Links in javadoc are replaced with qualified class names when necessary.
Replace constant interfaces with static imports

Remove constant interfaces and replace with static imports where the
static imports were necessary.