Assign PHIDs to PushLogs

Summary: Ref T4195. We need these in Herald, since HeraldTranscripts need to refer to a PHID which they acted upon.

Test Plan:
Ran migration, got PHIDs:

  mysql> select phid from repository_pushlog limit 3;
  +--------------------------------+
  | phid                           |
  +--------------------------------+
  | PHID-PSHL-25jnc6cjgzw5rwqgmr7r |
  | PHID-PSHL-2vrvmtslkrj5yv7nxsv2 |
  | PHID-PSHL-34x262zkrwoka6mplony |
  +--------------------------------+
  3 rows in set (0.00 sec)

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4195

Differential Revision: https://secure.phabricator.com/D7780
Add `rulePHID` to HeraldEffect

Summary: Ref T4195. Herald rules gained PHIDs only recently, propagate them to HeraldEffect to make some of the hook stuff eaiser.

Test Plan: iiam

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4195

Differential Revision: https://secure.phabricator.com/D7781
Add Herald support for blocking ref changes

Summary: Ref T4195. Allows users to write Herald rules which block ref changes. For example, you can write a rule like `alincoln can not create branches`, or `no one can push to the branch "frozen"`.

Test Plan:
This covers a lot of ground. I created and pushed a bunch of rules, then looked at transcripts, in general. Here are some bits in detail:

Here's a hook-based reject message:

  >>> orbital ~/repos/POEMS $ git push
  Counting objects: 5, done.
  Delta compression using up to 8 threads.
  Compressing objects: 100% (3/3), done.
  Writing objects: 100% (3/3), 274 bytes, done.
  Total 3 (delta 2), reused 0 (delta 0)
  remote: +---------------------------------------------------------------+
  remote: |      * * * PUSH REJECTED BY EVIL DRAGON BUREAUCRATS * * *     |
  remote: +---------------------------------------------------------------+
  remote:             \
  remote:              \                    ^    /^
  remote:               \                  / \  // \
  remote:                \   |\___/|      /   \//  .\
  remote:                 \  /V  V  \__  /    //  | \ \           *----*
  remote:                   /     /  \/_/    //   |  \  \          \   |
  remote:                   @___@`    \/_   //    |   \   \         \/\ \
  remote:                  0/0/|       \/_ //     |    \    \         \  \
  remote:              0/0/0/0/|        \///      |     \     \       |  |
  remote:           0/0/0/0/0/_|_ /   (  //       |      \     _\     |  /
  remote:        0/0/0/0/0/0/`/,_ _ _/  ) ; -.    |    _ _\.-~       /   /
  remote:                    ,-}        _      *-.|.-~-.           .~    ~
  remote:   \     \__/        `/\      /                 ~-. _ .-~      /
  remote:    \____(Oo)           *.   }            {                   /
  remote:    (    (--)          .----~-.\        \-`                 .~
  remote:    //__\\  \ DENIED!  ///.----..<        \             _ -~
  remote:   //    \\               ///-._ _ _ _ _ _ _{^ - - - - ~
  remote:
  remote:
  remote: This commit was rejected by Herald pre-commit rule H24.
  remote: Rule: No Branches Called Blarp
  remote: Reason: "blarp" is a bad branch name
  remote:
  To ssh://dweller@localhost/diffusion/POEMS/
   ! [remote rejected] blarp -> blarp (pre-receive hook declined)
  error: failed to push some refs to 'ssh://dweller@localhost/diffusion/POEMS/'

Here's a transcript, showing that all the field values populate sensibly:

{F90453}

Here's a rule:

{F90454}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4195

Differential Revision: https://secure.phabricator.com/D7782
Work around `hg` echoing warnings to stdout under --debug

Summary:
Ref T615. Ref T4237. With `--debug`, Mercurial will echo an "ignoring untrusted configuration option" warning **to stdout** if `.hgrc` has the wrong owner.

However, we need `--debug` to make `{parents}` usable, at least until the patches I got into the upstream are widely deployed. So after getting `--debug` output, strip off any leading warnings.

These warnings should always be in English, at least, since we set `LANG` explicitly.

Test Plan: Unit tests. @asherkin, maybe you can confirm this? I can't actually get the warning, but I think my `hg` in PATH is just a bit out of date.

Reviewers: asherkin, btrahan

Reviewed By: asherkin

CC: asherkin, aran

Maniphest Tasks: T615, T4237

Differential Revision: https://secure.phabricator.com/D7784