bitcoin-cli helpdetail to show full help for all RPCs

Prints to stdout a concatenation of full help text as if you had run
help on every RPC. This allows you to search help text when you
can't remember the name of an RPC.

src/rpc/server.cpp

@@ -101,7 +101,7 @@ std::string CRPCTable::help(const std::string& strCommand, const JSONRPCRequest&
     {
         const CRPCCommand *pcmd = command.second;
         std::string strMethod = pcmd->name;
-        if ((strCommand != "" || pcmd->category == "hidden") && strMethod != strCommand)
+        if ((strCommand != "" || pcmd->category == "hidden") && strMethod != strCommand && strCommand != "helpdetail")
             continue;
         jreq.strMethod = strMethod;
         try
@@ -127,6 +127,9 @@ std::string CRPCTable::help(const std::string& strCommand, const JSONRPCRequest&
                     strRet += "== " + Capitalize(category) + " ==\n";
                 }
             }
+            if (strCommand == "helpdetail") {
+                strRet += "== " + Capitalize(pcmd->category) + " ==\n";
+            }
             strRet += strHelp + "\n";
         }
     }