Use .netrc settings when making a connection

This may be useful to access a private repository protected using HTTP
basic authentication.

Requested by Brad Hilton.
Include the `extract` value when reporting illegal characters in it
Make running ocamlbuild directly easier

- Removed -cflags -g from arguments (we already turn on debug in the _tags file).
- Set default build directory in myocamlbuild.ml.
- Don't create static_0install.native link if invoked directly.
add autocompile support, controlled via --compile (default) and --no-compile
fixed diagnostic formatting for requires_compilation implementations