Trim package messages

makes it easier to layout in opam files
Consistent cleanup of temp files for parallel and seq processes
Allow pin --kind http, since it's now supported
Warnings and spelling
Fixed compat printer for 1.1

there still weren't enough parens
Merge pull request #1890 from OCamlPro/various-fixes

Fixes compat mode, some doc and spelling, allows pin --kind http
Implement mixed-mode VC pin

Closes #1868. Thanks a lot for the idea !
Document pin "mixed mode"
Fix mixed mode: sync the versionned files at source, not dest