Auto-instal of engines

I just equipped XBoard (not WinBoard) with an -autoInstall option,
which should still go into the 4.8.0 release. This option uses what I hope
will become the new standard for engine packages in Linux:

All engines should contain a 'plugin-spec' file <enginename>.eng, which they
should install in the directory /usr/share/games/plugins/<protocol>/ , where
<protocol> = uci, xboard, etc. The file will contain a magic sentence 
"plugin spec 0.0",
the command line needed to start the engine for the given protocol (e.g.
"pos --io-mode xboard") and possibly a working directory (as a preceding 
cd command),
a list of games / variant groups (like chess, chess960, capablanca, 
xiangqi, shogi, fairychess,
loserchess, checkers, go; the recognized game names will still have to 
be defined).

When -autoInstall is not an empty string, XBoard wil append any newly 
installed engines for UCI and XBoard protocol that it sees for the first 
time (as based on the modification date of the .eng file and the user 
settings file), to the -firstChessProgramNames list. The line will 
specify the corresponding -fcp, -fd arguments, and in case of UCI 
engines add a -fUCI flag. In this first implementation the variants list 
is ignored; in the future it could be matched with the -autoInstall list 
to decide which engines should be installed, and which should be 
ignored. (e.g. -autoInstall "shogi" could only install engines that play 
Shogi).

In the future the plugin-spec files could contain extra lines to give 
additional information, e.g. about known non-compliancy with the 
protocol (e.g. UCI engines that do not implement "searchmoves" or do not 
always repond to "isready"), or other peculiarities (e.g. whether they 
print the PV as long algebraic rather than SAN). XBoard could then add 
the applicable work-around options for these engine defects. (Like -fSAN 
to have the engine's PV converted to SAN, or -firstScoreAbs true for 
engines that report scores from whithe POV, etc.)