[PATCH] Portability fix for Solaris 10/x86

[PATCH] Portability fix for Solaris 10/x86

 * getdomainname unavailable there.
 * needs -lsocket for linkage.
 * needs __EXTENSIONS__ at the beginning of convert-objects.c

[JC: I've done this slightly differently from what Patrick originally
sent to the list and dropped the bit that deals with installations
that has curl header and library at non-default location.  I am
resisting the slipperly slope called autoconf.]

Signed-off-by: Junio C Hamano <junkio@cox.net>