src/key-func.c: Fix SCM_ASSERT call.

* src/key-func.c (guile_ssh_public_key_to_string): Fix SCM_ASSERT
  call.
src/Makefile.am (AM_LDFLAGS, AM_CFLAGS): Fix flags.

* src/Makefile.am (AM_LDFLAGS): Fix flags.
  (AM_CFLAGS): Likewise.  Add "-Wall" and "-g" flags.