Log Message:
port to exiv2 0.28.

upstream has moved on and these files no longer exist, so these patches
will be obsolete when krita itself is upgraded.

convert Exiv2::Value::AutoPtr to Exiv2::Value::UniquePtr.
convert Exiv2::AnyError to Exiv2::Error.
convert toLong() to toInt64().
convert size_ to size(), and pData_ to c_str() (c_data() might be OK
here, but the caller converts to char *).
convert locateIptcIrb() caller to use references not pointers.