passenger: remove wrapper scripts because they cause problems.

Instead, create a locations.ini so that Passenger can always find its own libraries.
passenger: remove curl dependency.

Although Passenger needs libcurl, libcurl is already installed by
default on OS X. Passenger does not need any particular version of
libcurl, so there's no need to depend on the Homebrew curl. Depending
on the Homebrew curl is useless anyway because its header and library
files are not in the compiler's default search paths.
nginx: show correct value for passenger_root in caveats.