Changed the way truncate is done to avoid reading to cache after the truncate.
Bug fixes.
Merge branch 's1543' of github.com:edwardchapin/cadcVOFS into s1543

Conflicts:
	vos/CadcCache.py
	vos/vos.py
Fixed merge conflicts.
Merge branch 's1543' of github.com:edwardchapin/cadcVOFS into s1543

Conflicts:
	vos/test/TestCadcCache.py
Fixed a bug which may have been causing issues.
Merge branch 's1543' of github.com:edwardchapin/cadcVOFS into s1543