sample nbits fix for invalidtxrequest.py

illustration_of_nbits_fix_that_passes_invalidtxrequest.patch

diff --git a/qa/rpc-tests/invalidtxrequest.py b/qa/rpc-tests/invalidtxrequest.py
index 26ca2f6..9fe6db4 100755
--- a/qa/rpc-tests/invalidtxrequest.py
+++ b/qa/rpc-tests/invalidtxrequest.py
@@ -15,6 +15,8 @@ import time
 In this test we connect to one node over p2p, and test tx requests.
 '''
 
+FORKHEIGHT=100  # to analyse fork interference
+
 # Use the ComparisonTestFramework with 1 node: only use --testbinary.
 class InvalidTxRequestTest(ComparisonTestFramework):
 
@@ -29,7 +31,7 @@ class InvalidTxRequestTest(ComparisonTestFramework):
     #                for now, set the forkheight to workaround this interference.
     def setup_network(self):
         self.nodes = start_nodes(1, self.options.tmpdir,
-                                 extra_args=[['-debug', '-whitelist=127.0.0.1', ]],
+                                 extra_args=[['-forkheight=%s' % FORKHEIGHT, '-debug', '-whitelist=127.0.0.1', ]],
                                  binary=[self.options.testbinary])
     # MVF-Core end
 
@@ -64,7 +66,8 @@ class InvalidTxRequestTest(ComparisonTestFramework):
         '''
         test = TestInstance(sync_every_block=False)
         for i in xrange(100):
-            block = create_block(self.tip, create_coinbase(height), self.block_time)
+            nbits = 0x207eeeee if i == (FORKHEIGHT-1) else 0x207fffff
+            block = create_block(self.tip, create_coinbase(height), self.block_time, nbits)
             block.solve()
             self.tip = block.sha256
             self.block_time += 1
diff --git a/qa/rpc-tests/test_framework/blocktools.py b/qa/rpc-tests/test_framework/blocktools.py
index 88f553a..ef8b54d 100644
--- a/qa/rpc-tests/test_framework/blocktools.py
+++ b/qa/rpc-tests/test_framework/blocktools.py
@@ -8,7 +8,7 @@ from mininode import *
 from script import CScript, OP_TRUE, OP_CHECKSIG
 
 # Create a block (with regtest difficulty)
-def create_block(hashprev, coinbase, nTime=None):
+def create_block(hashprev, coinbase, nTime=None, nbits=0x207fffff):
     block = CBlock()
     if nTime is None:
         import time
@@ -16,7 +16,7 @@ def create_block(hashprev, coinbase, nTime=None):
     else:
         block.nTime = nTime
     block.hashPrevBlock = hashprev
-    block.nBits = 0x207fffff # Will break after a difficulty adjustment...
+    block.nBits = nbits # default will break after a difficulty adjustment...
     block.vtx.append(coinbase)
     block.hashMerkleRoot = block.calc_merkle_root()
     block.calc_sha256()