eth int overflow: tests, mul support (#656)

* Move algorithm into ManticoreEVM

* Rm buggy unused line

* Initial eth testing setup

* Check for overflow in mul also

* clarifying comment

* Install solc for travis

* Add sudo

* x

* Rm travis_retry, since we rarely actually use it, and it's not available in this script for some reason

* Check for specific findings

* Fix test

* Clean up transaction firing logic

* Use less strict check, better for floating point

scripts/travis_install.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+function install_solc {
+    sudo wget -O /usr/bin/solc https://github.com/ethereum/solidity/releases/download/v0.4.19/solc-static-linux
+    sudo chmod +x /usr/bin/solc
+}
+
+install_solc
+
+pip install -U pip
+pip uninstall -y Manticore || echo "Manticore not cached"  # uninstall any old, cached Manticore
+pip install --no-binary keystone-engine -e .[dev]  # ks can have pip install issues