Moved UI calls to a new ui_handler interface
Don't use the non-portable -D flag to install

To make it work with BSD install(1) in addition to GNU install(1),
make sure to use "install -d && install" rather than install -D.
Added batch_ui

Used in --console mode when stderr isn't a tty. No progress indicator is
displayed.
Don't try to use GUI in --dry-run mode
Pass ui_handler to driver
Check GUI availability in make_ui
Fixed build for Debian's older Lwt
Replaced waitpid with waitpid_non_intr

Reported by Anders F Björklund.
Merge branch 'install' of https://github.com/afb/0install
Updated Windows build instructions
Moved scheme check to check redirects too
Link to Windows LWT patch in README
Don't ask Python for PackageKit candidates on Windows
Less verbose logging
Moved feed URL parsing to its own module
Simplified types in Feed_url
Use parsed feed URLs in more places

(found and fixed a bug setting the stability of distribution packages)
Migrated "0install search" to OCaml
Migrated "0install list" to OCaml
Migrated "0install list-feeds" to OCaml