Text groups for better compression

Change-Id: I42575d934d6b1edb77b355d10e9047fe54961c59
Removed check for trailing zero in decompressed string

With compressed groups, missing trailing zero is problematic.
On the other hand, added trailing zero is now okay.

Change-Id: Ia368b7ef2a198ee327029704e0a19f5b4ae7f84f
Fixed compilation on Linux by moving constants to .cpp

Change-Id: I76cec79142f3b2a85e36b8e61c8a780dc061dd66
Removed ChangeVisitor: it is not used anywhere

Change-Id: Ibeecdfe8f9f0768599c7df67367eebd7c82b1fd5
Group compression of diff dumps

Change-Id: I2d357218056f9324afa21d586c4b40d935b84830
Improved clearing of index caches

Change-Id: If8a035b4c4ea5b43a6d0bd8b39940d50fa261017
Don't write empty indexes

Change-Id: I94a394fd940b34a6654cc0f8ef841c191457cbf6
Don't use the override keyword for GCC 4.6

Change-Id: I32293346ba31fa90694f23a37500428658f52d31