wallet: wire -sendto into main(), where it never was (#119)

CmdSendTo() has been in walletcmd.cpp since #115 and nothing declared
it or called it. The flag was dead: `bitflash -sendto=ADDRESS,AMOUNT`
started a node and said nothing, because an unrecognised argument is
not an error here.

The v1.2.14 notes announce it under "A headless node can finally
spend", and the headless Linux binary is exactly the one that does not
have it -- `-help` there lists /newaddress and stops. The published
Windows binary does have it, because it was built from a working tree
that carried these two files uncommitted. So the artifacts disagree
with each other and neither matches the tag.

This adds only what was missing: the declaration in walletcmd.h, the
dispatch in main(), and the -help line. No behaviour change to
CmdSendTo itself.

Checked on a build of this branch, against a throwaway data directory:

  -help                          lists /sendto=ADDRESS,AMOUNT
  -sendto=NOTANADDRESS,1         "Not a valid address", exit 1
  -sendto=<valid>,-5             "Not a valid amount", exit 1
  -sendto=<valid>,999            refused on an empty wallet, exit 1

All five self-tests still pass.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/main_gui.cpp b/src/main_gui.cpp
index 1b72813..6164ad7 100644
--- a/src/main_gui.cpp
+++ b/src/main_gui.cpp
@@ -86,6 +86,8 @@ static void PrintUsage()
     printf("                              anyone, so guard it like cash)\n");
     printf("  /importwallet=FILE         (load keys from such a file back in)\n");
     printf("  /newaddress                (print the next receiving address, then exit)\n");
+    printf("  /sendto=ADDRESS,AMOUNT     (spend from this wallet, then exit -- the\n");
+    printf("                              only way to send without the window)\n");
     printf("  /newphrase                 (create a twelve-word recovery phrase for a\n");
     printf("                              wallet that has none, show it once, exit)\n");
     printf("  /restorephrase=\"WORDS\"     (rebuild this wallet from a phrase and scan\n");
@@ -388,6 +390,17 @@ int main(int argc, char* argv[])
         return nRet;
     }
 
+    // -sendto -- the counterpart to -newaddress. Without it a headless node can
+    // be paid and can never pay: SendMoney() has been here since 0.1.0 and only
+    // the window ever reached it.
+    string strSendTo = argval2(argc, argv, "/sendto", "-sendto");
+    if (!strSendTo.empty())
+    {
+        int nRet = CmdSendTo(strSendTo);
+        DBFlush(true);
+        return nRet;
+    }
+
     if (arg(argc,argv,"/recoveryaudit") || arg(argc,argv,"-recoveryaudit"))
     {
         int nRet = CmdRecoveryAudit();