Declare ocsigenserver as a 1.2 package

it uses an (uncommented) dev-repo field that triggered a warning on 1.1
this will also serve as a test of the new redirection/rewriting repo rules for 1.1 vs 1.2
Travis script: some changes

- test the specific changed package versions
- use autoremove
- simpler check for package availability
- replace 'grep | sed | grep | awk' with a single 'sed'
Update travis script to apply opam version compat before testing on <1.2
New version of ocaml-mstruct
Add merge queues and ropes
[mstruct] Update cstruct dep version
Add mirage-fs-unix.1.1.3
+ppx_tools.0.99.2
xmldiff 0.3.0 and 0.4.0 depend on camlp4
Milter requires OCaml < 4.02.0
Merge pull request #2886 from yallop/milter-ocaml-4.01

Milter 1.0.0 requires OCaml < 4.02.0
+cppo.1.0.0
mysql_protocol.1.0
Add depexts for ocamlgsl.
Merge pull request #2889 from slegrand45/master

mysql_protocol.1.0
Merge pull request #2887 from whitequark/cppo.1.0.0

+cppo.1.0.0
Merge pull request #2863 from samoht/master

Add merge queues and ropes
Merge pull request #2879 from samoht/mirage-fs

Add mirage-fs-unix.1.1.3
Merge pull request #2885 from yallop/xmldiff-camlp4

xmldiff 0.3.0 and 0.4.0 depend on camlp4
Added new Slacko release, 0.10.0