Fix python2 import (#93)

* too many underscores

* link with hpssgss too?

try an extra link option

* Revert "link with hpssgss too?"

This reverts commit fb6d96e.

pacifica/archiveinterface/backends/hpss/hpssExtensions.c

@@ -399,7 +399,7 @@ PyInit__hpssExtensions(void)
 #define INITERROR return
 
 void
-init__hpssExtensions(void)
+init_hpssExtensions(void)
 #endif
 {
 #if PY_MAJOR_VERSION >= 3