* guix/build/http.scm (open-connection-for-uri): New procedure.
(http-fetch): Use it. Pass the result as a #:port argument to
`http-get'.
Add hack to modify the `set-port-encoding!' binding in (web response).
* guix/ftp-client.scm (ftp-open): Add optional `port' parameter,
defaulting to 21. When calling `getaddrinfo', convert PORT to a
string and pass AI_NUMERICSERV when PORT is a number.
* guix/derivations.scm (imported-modules): New procedure.
(build-expression->derivation): New keyword argument `modules'.
Use `imported-modules' when MODULES is non-empty, and pass it with
`-L' to GUILE.
* guix/build/http.scm, guix/http.scm, tests/builders.scm: New files.
Ludovic Courtès