Nested write transactions are not supported.
Update changelog.txt
Update Realm.java
Update ImplicitTransaction.java
Style
Merge branch 'kg-protect-against-nested-transactions' of github.com:realm/realm-java into kg-protect-against-nested-transactions

Conflicts:
	realm/src/main/java/io/realm/internal/ImplicitTransaction.java
Merge branch 'master' of github.com:realm/realm-java into kg-protect-against-nested-transactions

Conflicts:
	changelog.txt
Merge pull request #455 from realm/kg-protect-against-nested-transactions

Nested write transactions are not supported.