Validation script now uses the right Ruby versions.

Squashed commit of the following:

commit 7f82fd770cbda3b81f3327f7ca6a593450e36bcc
Merge: e369128 6d8e618
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Fri May 16 14:17:45 2014 +0200

    Merge remote-tracking branch 'origin/next' into rca_validate_migrations

commit e3691282f507f21018ba763b7eeb1da01c1cef6c
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Fri May 16 14:17:31 2014 +0200

    Now it actually selects the right Rubies.

commit d317b0f03572acdeee34750afeb44db2380b99f3
Merge: e9396f3 abff119
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Fri May 16 10:03:41 2014 +0200

    Conflict resolution.

commit e9396f3a0a046b73e7a3850153c62da9e89a731c
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 18:59:47 2014 +0200

    .to_yaml missing otherwise.

commit ecc240bdd3f6dc099d411c5f33fc9e3618e64675
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 18:58:49 2014 +0200

    Remove pry again.

commit 0f8c23434f795c13354102d3f200377e4c6ea2b9
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 18:57:24 2014 +0200

    Log to some other place.

commit 5b8fc6528b66fb1a0e9b928c48bec7163bcd21e6
Merge: f83f773 e2e8ec3
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 18:45:05 2014 +0200

    Merge branch 'next' into rca_validate_migrations

commit f83f773961abbb35faf51e60eece31cf6725accd
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 18:25:26 2014 +0200

    One more supported version.

commit 14bc5476d5ef24dee288ce163bcce87382c3b88f
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 18:02:34 2014 +0200

    Better logging.

commit 804d2318cc0ebd07b0925fd39d52f5010df224cc
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 17:46:09 2014 +0200

    Skip combinations that won't work.

commit e3f348dc8316900f635cbc93c00464f8059d6668
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 17:38:48 2014 +0200

    Refining and handling some broken migrations.

commit 1128ff72ad2704016cf237ca32af9a317f160c38
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 15:20:44 2014 +0200

    More elegant checking.

commit d18cc997aea2c07dac4429e5de457c81cbf675f6
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 15:18:19 2014 +0200

    Wrong sequence of things, and mysql (1) support no longer necessary.

commit 6c7cd8340084c970f0181f1c3c2f35ba3018cfab
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 15:10:55 2014 +0200

    Fixed checking out different versions.

commit 0b20ee67b10c828262a2f74219d3e2ba1b10fd87
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 15:03:55 2014 +0200

    Add all our supported versions.

commit 178c84a647dd69462041b3947cd55580f6fb2ffb
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 14:45:16 2014 +0200

    First real working version.

commit 59cf6c469148a118f0feadb2cf6a1492ba0ebdf8
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 12:12:36 2014 +0200

    Now we're getting somewhere.

commit 73b67c085427c7f07f5c7fdfa6b08eadd0261571
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Thu May 15 10:44:33 2014 +0200

    More attempts that don't work.

commit 09d12c5a03bf4d7b3b9a1dfb659cbaee010e2a60
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Wed May 14 18:12:23 2014 +0200

    Work in progress on validating migrations.