Add test-driver to .gitignore
player: make "go" a system-only command

"go" was registered as a global player command, available everywhere.
However, a sanity assertion check enforced that a player could only use
it in a system (and not in planetary orbit or while docked), or yastg
would abort with:

yastg: player.c:245: cmd_hyper: Assertion `ship->postype == SYSTEM'
failed.
server: remove erroneous close()

Commit d666e07c, "server.c: Allow multiple listen sockets", replaced the
sockfd socket file descriptor with a linked list of sockets.
Unfortunately, the variable itself and the corresponding call to close()
at the end of server_main() were left behind.

When the server was shut down, it therefore tried to close an invalid
filehandle. Remove the erroneous variable and call to close().
Merge pull request #4 from gonzzor/gitignore

Add test-driver to .gitignore
.gitignore: add test/ptrlist_test

Commit e0b0a309, "test: add ptrlist_test", added a ptrlist test but
unfortunately forgot to add the test binary to .gitignore.
.gitignore: add test/*.trs

Newer autotools has a fancier test driver that produces some temporary
output files. These should be ignored.