Merge pull request #141 from orthez/index_slice

added method to return a slice of a matrix
added boolean and integer variables
added int test
disable mip tests for now
Merge branch 'master' of github.com:cvxgrp/cvxpy

* 'master' of github.com:cvxgrp/cvxpy:
  added method to return a slice of a matrix
fixed bugs with ecos and bool vars