fishdescriptor: .so can be loaded

fishdescriptor: .so can be loaded

(gdb) print (void*)dlopen("/u/iwj/things/chiark-utils.git/fishdescriptor/libfishdescriptor-donate.so.1.0",2)
$5 = (void *) 0x8f0d408
(gdb) print (void*)dlsym($5, "fishdescriptor_donate")
$6 = (void *) 0xf6953620 <fishdescriptor_donate>
(gdb) print (( int (*)(const char *, const int *) )$6)("/dev/enoent", (int[2]){0,-1})
$7 = 2
(gdb) print strerror(2)
$8 = 0xf74697e8 "No such file or directory"
(gdb)

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>