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
Added exn-source v0.1
add ojs-base 0.1.0
fix url md5
ojs-base: fix deps and package name
Fixed ocamlfind dependency
camomile.0.8.5: decouple from camlp4
Updated Lacaml
+Abella 2.0.2

Also removed abella.2.0.0, which is now obsolete
fix ojs-base md5sum
ojs-base depends on ppx_deriving_json < 2.0
Revert "Mark ppx_tools as unavailable on 4.03"
Merge pull request #2919 from ocaml/revert-2906-ppx_tools.compat

Revert "Mark ppx_tools as unavailable on 4.03"
Merge pull request #2911 from whitequark/camomile.no-camlp4

camomile.0.8.5: decouple from camlp4
Merge pull request #2909 from johnwhitington/master

Added exn-source v0.1
+utop.1.16
OASIS 0.4.5
Abella 2.0.2 requires OCaml 4.01.0+