Add missing period to DETAIL messages

Hi,

According to the error message style guide [1] "Detail and hint
messages: Use complete sentences, and end each with a period."

I found some DETAIL messages not following that period rule.

PSA a patch that fixes the missing period. In passing, I also fixed
some capitalization.

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[1] https://www.postgresql.org/docs/devel/error-style-guide.html#ERROR-STYLE-GUIDE-GRAMMAR-PUNCTUATION

Kind Regards,
Peter Smith.
Fujitsu Australia