Use String.concat in FailoverLoader for performance-critical concatenations of two Strings.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=54112486
Merge pull request #334 from cgruber/string_concat

Use String.concat in FailoverLoader for performance-critical concatenations of two Strings.
Merge branch 'master' into readwritelock

Conflicts:
	core/src/main/java/dagger/internal/FailoverLoader.java