pgsql: Add the missing cyrillic "Yo" characters ('e' and 'E' with two

Log Message:
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Add the missing cyrillic "Yo" characters ('e' and 'E' with two dots) to the
ISO_8859-5 <-> MULE_INTERNAL conversion tables.

This was discovered when trying to convert a string containing those characters
from ISO_8859-5 to Windows-1251, because we use MULE_INTERNAL/KOI8R as an
intermediate encoding between those two.

While the missing "Yo" was just an omission in the conversion tables, there are
a few other characters like the "Numero" sign ("No" as a single character) that
exists in all the other cyrillic encodings (win1251, ISO_8859-5 and cp866), but
not in KOI8R. Added comments about that.

Patch by Sergey Burladyan. Back-patch to 7.4.

Tags:
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REL8_1_STABLE

Modified Files:
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    pgsql/src/backend/utils/mb/conversion_procs/cyrillic_and_mic:
        cyrillic_and_mic.c (r1.11.2.1 -> r1.11.2.2)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/conversion_procs/cyrillic_and_mic/cyrillic_and_mic.c?r1=1.11.2.1&r2=1.11.2.2)