Use getprogname where available

getprogname.patch

diff --git a/configure b/configure
index 61c715d..1724ba2 100755
--- a/configure
+++ b/configure
@@ -50323,6 +50323,7 @@ for ac_func in \
     be32toh \
     fsync \
     futimens \
+    getprogname \
     getxattr \
     htonl \
     htons \
diff --git a/src/guestfs-internal-frontend.h b/src/guestfs-internal-frontend.h
index 9316421..9706df6 100644
--- a/src/guestfs-internal-frontend.h
+++ b/src/guestfs-internal-frontend.h
@@ -166,6 +166,8 @@ extern GUESTFS_DLL_PUBLIC int guestfs___add_libvirt_dom (guestfs_h *g, virDomain
  */
 #if HAVE_DECL_PROGRAM_INVOCATION_SHORT_NAME == 1
 #  define guestfs___program_name program_invocation_short_name
+#elif HAVE_GETPROGNAME
+#  define guestfs___program_name getprogname()
 #else
 #  define guestfs___program_name "libguestfs"
 #endif