chore(travis): add apt cache to .travis.yml
benchmarks: add control for quadcopter added
fix(tools/proofcheck/checker/func.ml): remove debugging info
chore(travis): fix gcc-version on OSX build (gcc-4.8.1)
tests(nra_ode): add Fedor's smt2s
benchmarks(hybrid_systems/crazyflie/stabilize.drh): add stabilizer.drh
fix(opensmt/egraph/Enode.C): update print_infix func to add parens for
the arg of pow function

CAPD generates a parsing error when it encouters

    x ^ -3

and asks us to provide

    x ^ (-3)
feat(cmake): add gflags, glog, json11 as external projects
fix(dsolvers/ode_solver): add debugging message
chore(.mailmap): add .mailmap
chore(travis): update travis (Linux & OSX)

 - separate test coverage build
 - introduce CTEST variable to order ctest
 - reduce test timeout to 450s from 500s
 - re-introduce delta* testcases
chore(travis): email to dreal-build@googlegroups
chore(cmake): use gflags when compile glog
feat(main.cpp): initialize glog
feat(dsolver/icp_solver): use glog
chore(cmake): add libunwind for Linux
fix(dsolvers/icp_solver): move LOG into the conditional
feat: use glog instead of util/logger.h
chore(cmake): suppress libunwind build warnings
feat: remove dsolver/util/logger