-WARNS6 cleanup (68 warnings)

-WARNS6 cleanup (68 warnings)
-No need to link in -ltermcap or -lcompat
-ANSI function declarations
-Remove (void) casts for unchecked function returns
-Rename local variables that shadow global declarations
-Actually check if read() and write() are successful, and act
	appropriately.  (taken from NetBSD)
-Use struct iovec and readv/writev in varpush() so that the function
	declaration isn't variable.  (taken from NetBSD)