add unit tests for GetMinFee
Revert "don't send feeless transactions"

This reverts commit 9a2f7a86fca6e243db7745cb1b15b35ce1b97b2e.
remove unit tests for new fee mode
Merge pull request #506 from langerhans/1.7-oldfee

Revert "don't send feeless transactions"
Merge pull request #503 from leofidus/fee-tests

add unit tests for GetMinFee