Getting MASTER_SITES for sourceforge ports more easily

[Alexander Churanov]

Folks,

Thank you for clarifications. Fetching just works if MASTER_SITES are
SF/something.

The correct URI may be viewed just using the browser. I've started
downloading a file from SF, then paused the download, examined the actual
URI the file is downloaded from and verified that URIs generated by
Makefiles for my ports are correct.

Alexander Churanov,
maintainer of devel/boost-*