Upgrade serde

[SimonSapin]

This will enable using serde-rs/serde#1191 in Servo

Includes a rebase of serde-rs/serde@master...Gankro:deserialize_from_enums4

---

This change is 

[SimonSapin]

@bors-servo try

[bors-servo]

⌛ Trying commit 734822b with merge 497dd30...

[bors-servo]

💔 Test failed - status-taskcluster

[SimonSapin]

The log ends as below. Does this mean Cargo is missing?

tidy reported no errors.
Traceback (most recent call last):
  File "script/headless.py", line 68, in <module>
    subprocess.check_call(['cargo', 'build', '--release', '--verbose', '--features', 'headless'])
  File "/usr/lib/python2.7/subprocess.py", line 536, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 523, in call
    return Popen(*popenargs, **kwargs).wait()
  File "/usr/lib/python2.7/subprocess.py", line 711, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1343, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory
[taskcluster 2018-03-27 09:05:04.829Z] === Task Finished ===
[taskcluster 2018-03-27 09:05:04.829Z] Unsuccessful task run with exit code: 1 completed in 389.522 seconds

[glennw]

The log also contains:

curl: (7) Failed to connect to sh.rustup.rs port 443: Connection timed out

[glennw]

So, I guess a temporary network failure?

[SimonSapin]

Ah thanks, I’d missed that.

@bors-servo try retry

[bors-servo]

⌛ Trying commit 734822b with merge 1a12a10...

[bors-servo]

☀️ Test successful - status-appveyor, status-taskcluster
State: approved= try=True

[emilio]

@bors-servo r+

[bors-servo]

📌 Commit 1669ec2 has been approved by emilio

[bors-servo]

⌛ Testing commit 1669ec2 with merge 7ef6084...

[bors-servo]

💔 Test failed - status-taskcluster

[SimonSapin]

Cloning into 'webrender'...
fatal: reference is not a tree: 7ef6084e3615f389de876f1bf1954de797182bbe

@bors-servo r=emilio

[bors-servo]

📌 Commit beebcd9 has been approved by emilio

[bors-servo]

⌛ Testing commit beebcd9 with merge 97a39b3...

[bors-servo]

☀️ Test successful - status-appveyor, status-taskcluster
Approved by: emilio
Pushing 97a39b3 to master...