fixed subsidy limit test
fix documentation of block reward schedule

there was an off-by-one error in the documentation
Merge pull request #490 from leofidus/1.7-subsidy-limit-test

fixed subsidy limit unittest
Disable payment protocol pending further assessment and potential rework.
Replaced tabs with spaces.
Merge pull request #491 from rnicoll/1.7-dev-no-payment

Disable payment protocol pending further assessment and potential rework