renamed index distinction:
internal -> composite
external -> mixed
for storage backends with tx isolation, all changes including schema changes are committed in one go due to atomic guarantee.
Merge branch 'titan05' of https://github.com/thinkaurelius/titan into titan05

Conflicts:
	titan-test/src/main/java/com/thinkaurelius/titan/testutil/gen/Schema.java
renamed methods after conflict resolution
fixed test case after changing commit behavior