fixed some packaging issues for 6L38

This fixes a bunch of little nits: removes GNUMake dependencies from Makefile.ams, removes some other Makefile.am warnings by setting subdir-objects, sets DEB_BUILD_MAINT_OPTIONS to hardening=-format to suppress some more warnings. Hope it helps.

Thanks huge for gnome-inform7.
This didn't work during `make distcheck` when `$(distdir)` didn't exist yet; I used
```sh
`(mkdir -p $(distdir) && cd $(distdir) && pwd)`
```
but for all I know there might be a better way to canonicalize paths in bash.