pgsql: Clarify comments in enforce_generic_type_consistency().

Clarify comments in enforce_generic_type_consistency().

Some of the pre-existing comments were vague about whether they
referred to all polymorphic types or only the old-style ones.

Also be more consistent about using the "family 1" vs "family 2"
terminology.

Himanshu Upadhyaya and Tom Lane

Discussion: https://postgr.es/m/CAPF61jBUg9XoMPNuLpoZ+h6UZ2VxKdNt3rQL1xw1GOBwjWzAXQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/53367e6c62e3111eccdd578a3fa607c48c3e1fb6

Modified Files
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src/backend/parser/parse_coerce.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)