travis: Install sphinx and msgcheck only for the build running runonce.

Squashed commit of the following:

commit 3b528b5f103500d9cfa62e3442d7c977ee7c6259
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 10:24:02 2014 +0300

    .travis.runonce.bash: fix travis check

    * Install sphinx & msgcheck on same line.
    * Don't install sphinx twice.

commit aca2040807b082a1b1f74be4f8f3917407dd4e3c
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 01:12:10 2014 +0300

    .travis.runonce.bash: use sudo in travis

commit 00b8d9d0b269679867d3ef2d730274d6b0d1701b
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 01:08:51 2014 +0300

    Revert ".travis.runonce.bash: improvising"

    This reverts commit 373471845cd2a1ebfc615fe0eb253ac5f169ec67.

commit 373471845cd2a1ebfc615fe0eb253ac5f169ec67
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 01:00:52 2014 +0300

    .travis.runonce.bash: improvising

    I hope this also works with Travis, but I have no idea does whereis
    usually check $HOME/.local/bin …

commit 1a8f54f337455dbb3e5643ce8fa9735183edcd79
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 00:46:16 2014 +0300

    Revert ".travis.runonce.bash: adjust $PATH"

    This reverts commit dc096462798499270e78ed7aa596dade938796a4.

commit dc096462798499270e78ed7aa596dade938796a4
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 00:37:13 2014 +0300

    .travis.runonce.bash: adjust $PATH

    If something is already installed elsewhere, pip won't reinstall it.

commit bd34aae08a8a739c7f6ecd8db685dc81ac3acf7d
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 00:25:56 2014 +0300

    .travis.runonce.bash: use full paths

    for applications installed to $HOME/.local

commit 643878c2f94cbe9f7244a4d8df7463ed25af2275
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 00:24:20 2014 +0300

    Fix Python 2.6 build

    Move msgcheck & sphinx to .travis.runonce.bash so 2.6 doesn't fail to
    msgcheck requiring Python 2.6.

commit 2fbb279ac26b304ad976b2e04dd7d60718d4521e
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 00:19:30 2014 +0300

    fix .travis.yml

commit cc1ccb15a0178e5606cfcc042682dba50833abed
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 00:08:12 2014 +0300

    .travis.runonce.bash: add msgcheck

    && requirements.txt: add msgcheck & forgotten sphinx.

commit a2d910d2f50022a4f75e5d87d52b2f9176046ecb
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 00:03:41 2014 +0300

    .travis.runonce.bash: add forgotten sphinx

commit cdd564f1157ae18e753b0a1da269cdc3421f1f22
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Sat Jul 5 00:01:14 2014 +0300

    Break .travis.yml to two files

    * .travis.yml = the primary Travis config file.
    * .travis.runonce.bash = the script which we want to run only once per
    build.

commit 6c3d2dfcd2033c6ed488ad67068ad7deff0c9c95
Merge: ebf2442 37d8a54
Author: Valentin Lorentz <progval+github@progval.net>
Date:   Fri Jul 4 19:06:47 2014 +0200

    Merge pull request #755 from Mkaysi/services

    Services: default NickServ and ChanServ to NickServ and ChanServ.

commit ebf2442dbc7d10205c6311ba0b95d26660088046
Merge: 3f9b10c c534e82
Author: Valentin Lorentz <progval+github@progval.net>
Date:   Mon Jun 30 13:27:34 2014 +0200

    Merge pull request #762 from Mkaysi/nickauth

    NickAuth: update l10n-fi & messages.pot .

commit c534e824f03f3f01ba969fbab4ddb9267d5c30fa
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Mon Jun 30 14:22:34 2014 +0300

    NickAuth: update l10n-fi & messages.pot .

    [SKIP CI]

commit 3f9b10cc5983161ff61ac6584a4c728ca8596d0e
Merge: 607e5e0 38b933a
Author: Valentin Lorentz <progval+github@progval.net>
Date:   Mon Jun 30 13:17:13 2014 +0200

    Merge pull request #761 from nyuszika7h/fix-nickauth-nick-list-error

    NickAuth: fix error message in !list

commit 38b933aee96c0305f603169f365721e2cd766764
Author: nyuszika7h <nyuszika7h@gmail.com>
Date:   Mon Jun 30 09:50:43 2014 +0200

    NickAuth: fix previous commit

    I'm too used to JavaScript.

commit 8e97ad37075ce69f2332a14ed400408650896bff
Author: nyuszika7h <nyuszika7h@gmail.com>
Date:   Mon Jun 30 09:47:55 2014 +0200

    NickAuth: fix error message in !list

commit 37d8a545e969914caa97a68af54f93148e36ca4c
Author: Mikaela Suomalainen <mikaela.suomalainen@outlook.com>
Date:   Fri Jun 6 13:54:26 2014 +0300

    Services: default NickServ and ChanServ to NickServ and ChanServ.

    * Most of networks have services with this name.
        * I can only name QuakeNet from those that don't, but the default
        configuration exludes it.
    * If this plugin is loaded in Supybot-wizard, it asks for nicknames of
    NickServ and ChanServ.

    [SKIP CI] because this is `git commit --amend` and the build already
    passed.