Update the protocol buffer library to use Int64 from the fixnum package

Update the protocol buffer library to use Int64 from the fixnum package

The 64-bit integers in protocol buffer messages now use the Int64
object from the fixnum package for representing 64-bit integers
instead of an 8-byte binary buffer.

When generating JSON the 64-bit integers in the 53-bit range are
written as integers. Larger integeres are still written as strings.

R=sigmund@google.com
BUG=

Committed: https://github.com/dart-lang/protobuf/commit/822b4cf

[Søren Gjesse, 2013-10-02 14:02:02]

This goes hand in hand with https://chromiumcodereview.appspot.com/25708003.

[Søren Gjesse, 2013-10-04 07:00:09]

Friendly ping.

[Siggi Cherem (dart-lang), 2013-10-04 17:58:03]

lgtm

sorry for the delay, I'm still catching up =)

[Søren Gjesse, 2013-10-07 06:51:28]

Committed patchset #2 manually as r822b4cf (presubmit successful).