Fix submodule init on clone

In a previous pull request, clone was changed to initialize and update
submodules recursively.  This change used a flag, --recurse-
submodules, that was added after the version of git being used by the
dea.  This flag was actually an alias to --recursive which does exist
in the version of git used by the dea[1].

The fix made for the previous failure was to split the clone command
into two calls (clone, then change directory and initialize
submodules) which was unnecessary.  In addition, this fix added some
logic around cloning with --depth=1 that broke this depth
functionality when cloning with http:// URLs (the default when using
GitHub).

This change has the net effect of reverting the changes in
20bcb31275e1605d626fb1869dc9fb8314252dd0 and doing this simplest
possible fix for the --recurse-submodules change.  Specifically this
change rolls back the changes around --depth=1 as they are not
necessary to fix the problem with the unsupported flag and break the
functionality that --depth=1 was intended to provide.

[1] The options clone supports in the version of Git on the dea

-----> Downloaded app package (23M)
-----> Downloaded app buildpack cache (4.0K)
error: unknown option `recurse-submodules'
usage: git clone [options] [--] <repo> [<dir>]

    -q, --quiet           be quiet
    -v, --verbose         be verbose
    --progress            force progress reporting
    -n, --no-checkout     don't create a checkout
    --bare                create a bare repository
    --mirror              create a mirror repository (implies bare)
    -l, --local           to clone from a local repository
    --no-hardlinks        don't use local hardlinks, always copy
    -s, --shared          setup as shared repository
    --recursive           initialize submodules in the clone
    --template <path>     path the template repository
    --reference <repo>    reference repository
    -o, --origin <branch>
                          use <branch> instead of 'origin' to track upstream
    -b, --branch <branch>
                          checkout <branch> instead of the remote's HEAD
    -u, --upload-pack <path>
                          path to git-upload-pack on the remote
    --depth <depth>       create a shallow clone of that depth

/var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:33:in `clone_buildpack': Failed to git clone buildpack (RuntimeError)
	from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:41:in `build_pack'
	from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:26:in `block in compile_with_timeout'
	from /usr/lib/ruby/1.9.1/timeout.rb:68:in `timeout'
	from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:25:in `compile_with_timeout'
	from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:16:in `block in stage_application'
	from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:12:in `chdir'
	from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:12:in `stage_application'
	from /var/vcap/packages/dea_next/buildpacks/bin/run:10:in `<main>'
Merge pull request #25 from nebhale/50081011-recursive

Fix submodule init on clone