This method dates back from the beginnings of Erlang.mk
and should not have been used for around a decade by now.
Adding "git" to the offending dep lines is enough to upgrade.

This should both be more solid and more secure.

Erlang.mk will no longer feature packages out of the box,
except for the applications that we implement plugins for
(such as erlydtl, proper or relx) and the projects I work
on that are also used to test Erlang.mk (cowboy and friends).

This is a breaking change. In most cases the fix is to add
a full dep_* line for the dependencies that were used as
packages before.

The tests were waiting for the test group to finish before
they could continue with the next test group. Now "core"
and "all" targets directly depend on individual test cases,
allowing parallel Make to get to the next tests quicker and
removing 1/3rd of the total run time.

  make check -j8 -k  5790,16s user 1207,08s system 627% cpu 18:35,49 total
  make check -j8 -k  6250,13s user 1326,77s system 972% cpu 12:59,16 total

We now provide the version as a tagged tuple indicating
whether this is a branch, tag or ref. This should help
rebar automatically upgrade dependencies, and remove
an annoying warning when rebar is used.

In order to detect the type of version the dependencies
must be available, therefore the rebar.config target now
depends on the deps target.

To test this the Cowboy package version had to be changed
from 1.0.4 to master. This is a breaking change, but I do
not expect too many people to still use 1.0.4.

Instead of calling `find` we use $(wildcard ...) and some
logic on top to find all the files we are looking for.

This is more efficient and greatly helps reduce re-build
times when there's little to be done, particularly when
many dependencies are involved.

It's become hard to find a host that provides Subversion.