Adds .gitignore rules for files generated by autoreconf

When running `autoreconf -fvi`, several files were generated
that were not ignored by the existing .gitignore rules:
```
aclocal.m4 configure m4/libtool.m4 m4/ltoptions.m4 m4/ltsugar.m4
m4/ltversion.m4 m4/lt~obsolete.m4
```

Also, after a successful build, `git status` reports on the built binaries:
```
        src/baton-chmod
        src/baton-get
        src/baton-list
        src/baton-metamod
        src/baton-metaquery
        src/baton-metasuper
```
All should now be ignored by the updated .gitignore