CH02::tx propagation: use "full node" and "lightweight client"

Per the updated infobox in CH01, we stop using the name "clients" for
full nodes; they're peers.  We also clarify that miners commit effort to
blocks rather than necessary prove them valid.

ch02.asciidoc

@@ -471,8 +471,8 @@ blocks are added.
 ((("propagation", "process of")))Because the transaction contains all
 the information necessary to process, it does not matter how or where it
 is transmitted to the Bitcoin network. The Bitcoin network is a
-peer-to-peer network, with each Bitcoin client participating by
-connecting to several other Bitcoin clients. The purpose of the Bitcoin
+peer-to-peer network, with each Bitcoin peer participating by
+connecting to several other Bitcoin peers. The purpose of the Bitcoin
 network is to propagate transactions and blocks to all participants.
 
 ===== How it propagates
@@ -690,14 +690,15 @@ image::images/mbc2_0209.png["Alice's transaction included in a block"]
 (SPV)")))((("simple-payment-verification (SPV)")))Now that Alice's
 transaction has been embedded in the blockchain as part of a block, it
 is part of the distributed ledger of Bitcoin and visible to all Bitcoin
-applications. Each bitcoin client can independently verify the
-transaction as valid and spendable. Full-node clients can track the
-source of the funds from the moment the bitcoin were first generated in
-a block, incrementally from transaction to transaction, until they reach
+applications. Each bitcoin full node can independently verify the
+transaction as valid and spendable. Full nodes validate every transfer
+of the funds from the moment the bitcoin were first generated in
+a block through each subsequent transaction until they reach
 Bob's address. Lightweight clients can do what is called a simplified
 payment verification (see <<spv_nodes>>) by confirming that the
 transaction is in the blockchain and has several blocks mined after it,
-thus providing assurance that the miners accepted it as valid.
+thus providing assurance that the miners expended significant effort
+committing to it.
 
 Bob can now spend the output from this and other transactions. For
 example, Bob can pay a contractor or supplier by transferring value from