Merge pull request ethereum#4028 from ethereum/eip198

EIP198 - Bigint modexp precompiled contract

Deleted .submodules file. There are none.

Fix syntax errors.

Removed Yosemite and El Capitan runs.

We now only produce Mavericks binaries, because those build steps run so much faster.
Yosemite and El Capitan via VMWare on 2009 era Mac Book Pros just cannot complete in time.
Now attempting to run all the unit-tests again, to see if we can get them reliable.

Reordered the GPL message sections.

Untagged builds appearing.

Let's see if I can filter them out.

And then carry on.

Clear out cpp-ethereum cache.

Merge pull request ethereum#5 from bobsummerwill/ci_fixes

My syntax was previously incorrect for multiple ENV settings.

Merge pull request ethereum#4 from bobsummerwill/ci_fixes

Forgot to copy the updated release.sh script across too.