solfege uses pkg-config

Closes #17775.
lighttpd: optional dep on libev
lighttpd: enable some free options
libev and libevent conflict
mercurial: Use opt_prefix in caveat

The caveat mentioned that the `hgext` directory was
in the Cellar.  A better path is the `opt_prefix` path
because it doesn't change when the mercurial is updated.

Closes #17773.
Closes #17779.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
Avoid nil in URL specs
Remove dead code

This code only existed to support very old formula syntax, which was
otherwise removed in e6b97bebd99779b52462dcd387191d804fc95b93.
Establish a convention for Requirement names

The name attribute of requirements is used when generating options for
the :optional and :recommended dependency tags.

Unless otherwise specified, the name attribute of a Requirement will be
populated by stripping any module prefixes from the beginning and
"Dependency" or "Requirement" from end of the class name and downcasing
the result.