* moved CtdlDecodeQuotedPrintable() into tools.c

* moved CtdlDecodeQuotedPrintable() into tools.c
  (later we will move most or all of tools.c into libcitadel)
* amended citadel_ipc.c message reading loop.  When using MSG4 (nearly
  always), parse base64 and quoted-printable encodings, and decode them.
  MSG4 does not *yet* send these, instead performing the decoding on
  the server side.  During experimentation I told the server not to
  decode, and this will resolve Bug #289.  All that's left to do is to
  add something to the protocol so that the client can tell the server
  that it wants non-decoded message text.  I'll do that tomorrow.