Fix the testsuite for the new fields in the ocamlbuild plugin
Fix the testsuite
OCamlbuild: Don't use -plugin-tags if XOCamlbuildPluginTags in not set
OCamlbuild: Use OCamlVersion instead of the current compiler version
Document OASISVersion.comparator_ge
OCamlbuild: Fixing doc compilation
OCamlbuild: Warn when XOCamlbuildPluginTags is used while the OCaml version is not restricted
OCamlbuild: Use opt string instead of string for PluginTags
OCamlbuild: Add descriptions to the new fields
OCamlbuild: Add an example for the new fields
OCamlbuild: Fix the warning about -plugin-tags
Merge pull request #24 from jpdeplaix/master

Some fixes related to global fields PluginTags and ExtraArgs.