added option for work-around for some FRC engines in regards to FRCFENs

added option for work-around for some FRC engines in regards to FRCFENs

It suddenly occurred to me that I had promised on CCC to include an option to provide a work-around for the problem that some FRC engines do not understand FRC FENs (and thus do not play at all under WinBoard, as FRC always has to begin with sending the initial position).

So I added the options -firstNeedsNoncompliantFEN, -secondNeedsNoncompliantFEN. This affects winboard.c and xboard.c, (for defining the option), common.h, backend.h, backend.c, (for implementing it), xboard.texi and winboard.rtf (decribing it). This option provides users with a means to always force the FEN castling field to KQkq (but can be used for many other work-arounds as well).