values smaller than 0.001 sat/B can't be represented by CFeeRate, but they are not rejected.

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.0009

error code: -6
error message:
Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)
```

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.000000000009

error code: -3
error message:
Invalid amount

BOOST_CHECK(ParseMoney("1   ", ret));
    BOOST_CHECK_EQUAL(ret, COIN);
    BOOST_CHECK(ParseMoney("  1 ", ret));
    BOOST_CHECK_EQUAL(ret, COIN);
    BOOST_CHECK(ParseMoney("0.1", ret));
    BOOST_CHECK_EQUAL(ret, COIN/10);
    BOOST_CHECK(ParseMoney("0.01", ret));
    BOOST_CHECK_EQUAL(ret, COIN/100);
    BOOST_CHECK(ParseMoney("0.001", ret));
    BOOST_CHECK_EQUAL(ret, COIN/1000);
    BOOST_CHECK(ParseMoney("0.0001", ret));
    BOOST_CHECK_EQUAL(ret, COIN/10000);
    BOOST_CHECK(ParseMoney("0.00001", ret));
    BOOST_CHECK_EQUAL(ret, COIN/100000);
    BOOST_CHECK(ParseMoney("0.000001", ret));
    BOOST_CHECK_EQUAL(ret, COIN/1000000);
    BOOST_CHECK(ParseMoney("0.0000001", ret));
    BOOST_CHECK_EQUAL(ret, COIN/10000000);
    BOOST_CHECK(ParseMoney("0.00000001", ret));
    BOOST_CHECK_EQUAL(ret, COIN/100000000);
    BOOST_CHECK(ParseMoney(" 0.00000001 ", ret));
    BOOST_CHECK_EQUAL(ret, COIN/100000000);
    BOOST_CHECK(ParseMoney("0.00000001 ", ret));
    BOOST_CHECK_EQUAL(ret, COIN/100000000);
    BOOST_CHECK(ParseMoney(" 0.00000001", ret));
    BOOST_CHECK_EQUAL(ret, COIN/100000000);
    
    BOOST_CHECK(!ParseMoney("0.000000001", ret));
    
    BOOST_CHECK(!ParseMoney("", ret));