Allow building if popt isn't available.

Allow building if popt isn't available.

The changes are to:
- remove unnecessary include in libmapiadmin
- only build mapistore test tool if popt is available
- only build torture tests if popt is available.

The last change could be finer (e.g. only leaving out the
part of the torture test that actually requires popt) but
that seemed more fragile and generally unnecessary.

Resolves ticket #233.