[Bug]: `plural()` incorrectly pluralizes certain compound terms

Hello and kudos for the great library!
I've encountered the following issue, which is breaking my pipeline.

```
import inflect

_infl = inflect.engine()
_infl.plural("Old technology") # 'Old technologys'
```
while

```
import inflect

_infl = inflect.engine()
_infl.plural("technology") # 'technologies'
```

Would you be open to supporting it or do you have a different opinion/view?
I also noticed some issues with pluralizing capitalized terms, but I saw there’s already an open issue for that (https://github.com/jaraco/inflect/issues/201).

Thank you!

## UPDATE
So, I've noticed that the lowered version works, so perhaps the issue falls under the scope of the one referenced above.

```
import inflect

_infl = inflect.engine()
_infl.plural("old technology") # 'old technologies'
```

Start with the public plural() entry point and reproduce the difference between "Old technology" and "technology" shown in the issue. Compare it with the lower-case compound example and the referenced capitalized-terms issue; done means the compound term is pluralized correctly without regressing the existing behavior.

Written by the indexing model from the issue text.