Eliminating Inconsistencies in Textual Output

There were discrepancies between usage of "block chain" and "blockchain", I've changed them to the latter. The reason for this was that Wikipedia when describing this data structure writes "A blockchain — *originally block chain*", so it seemed the more appropriate term.

src/rpc/blockchain.cpp

@@ -151,7 +151,7 @@ UniValue getblockcount(const JSONRPCRequest& request)
     if (request.fHelp || request.params.size() != 0)
         throw runtime_error(
             "getblockcount\n"
-            "\nReturns the number of blocks in the longest block chain.\n"
+            "\nReturns the number of blocks in the longest blockchain.\n"
             "\nResult:\n"
             "n    (numeric) The current block count\n"
             "\nExamples:\n"
@@ -168,7 +168,7 @@ UniValue getbestblockhash(const JSONRPCRequest& request)
     if (request.fHelp || request.params.size() != 0)
         throw runtime_error(
             "getbestblockhash\n"
-            "\nReturns the hash of the best (tip) block in the longest block chain.\n"
+            "\nReturns the hash of the best (tip) block in the longest blockchain.\n"
             "\nResult\n"
             "\"hex\"      (string) the block hash hex encoded\n"
             "\nExamples\n"
@@ -1027,7 +1027,7 @@ UniValue getblockchaininfo(const JSONRPCRequest& request)
     if (request.fHelp || request.params.size() != 0)
         throw runtime_error(
             "getblockchaininfo\n"
-            "Returns an object containing various state info regarding block chain processing.\n"
+            "Returns an object containing various state info regarding blockchain processing.\n"
             "\nResult:\n"
             "{\n"
             "  \"chain\": \"xxxx\",        (string) current network name as defined in BIP70 (main, test, regtest)\n"