Revert "remove chrono/timer for <1.48 boost"

This reverts commit b0bb402eeb290056a92ffebac66957369b91f67c.
Revert "make primeminer rpool.net compatible (ie, submitting 6' shares too)"

This reverts commit 04460cc11faa1941ef14afef7c4ed9bdd0d1b8c0.