This adds a -regetest-only undocumented (for regression testing only)
command-line option -blockversion=N to set block.nVersion.
Adds to the "has the rest of the network upgraded to a
block.nVersion we don't understand" code so it calls
-alertnotify when 51 of the last 100 blocks are up-version.
But it only alerts once, not with every subsequent new, upversion
block.
And adds a forknotify.py regression test to make sure it works.
Tested using forknotify.py:
Before adding CAlert::Notify, get:
Assertion failed: -alertnotify did not warn of up-version blocks
Before adding code to only alert once:
Assertion failed: -alertnotify excessive warning of up-version blocks
After final code in this pull:
Tests successful
