Fixed runtime error on older gcc/g++ (<4.9) where std::reg_ex is non-standards compliant and produced a regex compile fail. This new simpler regex does not trip up even broken libstdc++ std::regex implementations.
Summary: Fixes phabricator issue T56
Test Plan: make check on Ubuntu 14.04 / 14.05 (Travis equivalent)
Reviewers: #bitcoin_abc, deadalnix, freetrader, sickpig, kyuupichan, awemany, O1 Bitcoin ABC
Reviewed By: #bitcoin_abc, deadalnix, O1 Bitcoin ABC
Differential Revision: https://reviews.bitcoinabc.org/D290