Dev Docs: REST: Add Security Note & Reindex Note

Added both notes to both JSON-RPC and REST docs.

Suggested by Jonas Schnelli (thanks!)

_includes/helpers/vars.md

@@ -73,3 +73,5 @@ bitcoins even if this parameter is set to `1` or higher.{% endcapture %}
 {:.ntpd}{% endcapture %}
 
 {% assign WARNING="![Warning icon](/img/icons/icon_warning.svg) **Warning:**" %}
+
+{% assign reindexNote="Note: if you begin using `txindex=1` after downloading the block chain, you must rebuild your indexes by starting Bitcoin Core with the option  `-reindex`.  This may take several hours to complete, during which time your node will not process new blocks or transactions. This reindex only needs to be done once." %}

_includes/ref/bitcoin-core/rest/intro.md

@@ -16,6 +16,9 @@ port 18332 for testnet. It must be enabled by either starting Bitcoin
 Core with the `-rest` option or by specifying `rest=1` in the
 configuration file.
 
+The interface is not intended for public access and is only accessible
+from localhost by default.
+
 {{WARNING}} A web browser can access a HTTP REST interface running on
 localhost, possibly allowing third parties to use cross-site scripting
 attacks to download your transaction and block data, reducing your

_includes/ref/bitcoin-core/rest/requests/get_tx.md

@@ -13,6 +13,8 @@ http://opensource.org/licenses/MIT.
 
 The `GET tx` operation {{summary_restTx}}
 
+{{reindexNote}}
+
 *Request*
 
 {% highlight text %}

_includes/ref/bitcoin-core/rpcs/rpcs/getrawtransaction.md

@@ -13,6 +13,8 @@ http://opensource.org/licenses/MIT.
 
 The `getrawtransaction` RPC {{summary_getRawTransaction}}
 
+{{reindexNote}}
+
 *Parameter #1---the TXID of the transaction to get*
 
 | Name               | Type            | Presence                    | Description

_includes/ref_core_rpc_intro.md

@@ -119,6 +119,9 @@ Page][devexamples] for details. JSON-RPC starts on port 8332 for mainnet
 and 18332 for testnet and regtest. By default, `bitcoind` doesn't use a
 JSON-RPC user, but you can set one (see `bitcoind --help`).
 
+The interface is not intended for public access and is only accessible
+from localhost by default.
+
 RPCs are made using the standard JSON-RPC 1.0 syntax, which sends several
 standard arguments: