Fix citext upgrade script for disallowance of oidvector element assignment.

In commit 45e02e3232, we intentionally
disallowed updates on individual elements of oidvector columns.  While that
still seems like a sane idea in the abstract, we (I) forgot that citext's
"upgrade from unpackaged" script did in fact perform exactly such updates,
in order to fix the problem that citext indexes should have a collation
but would not in databases dumped or upgraded from pre-9.1 installations.

Even if we wanted to add casts to allow such updates, there's no practical
way to do so in the back branches, so the only real alternative is to make
citext's kluge even klugier.  In this patch, I cast the oidvector to text,
fix its contents with regexp_replace, and cast back to oidvector.  (Ugh!)

Since the aforementioned commit went into all active branches, we have to
fix this in all branches that contain the now-broken update script.

Per report from Eric Malm.

contrib/citext/citext--unpackaged--1.0.sql

@@ -105,7 +105,12 @@ UPDATE pg_catalog.pg_attribute SET attcollation = 100
 FROM typeoids
 WHERE atttypid = typeoids.typoid;
 
-UPDATE pg_catalog.pg_index SET indcollation[0] = 100
+-- Updating the index indcollations is particularly tedious, but since we
+-- don't currently allow SQL assignment to individual elements of oidvectors,
+-- there's little choice.
+
+UPDATE pg_catalog.pg_index SET indcollation =
+  pg_catalog.regexp_replace(indcollation::pg_catalog.text, '^0', '100')::pg_catalog.oidvector
 WHERE indclass[0] IN (
   WITH RECURSIVE typeoids(typoid) AS
     ( SELECT 'citext'::pg_catalog.regtype UNION
@@ -115,7 +120,8 @@ WHERE indclass[0] IN (
   WHERE opcintype = typeoids.typoid
 );
 
-UPDATE pg_catalog.pg_index SET indcollation[1] = 100
+UPDATE pg_catalog.pg_index SET indcollation =
+  pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[1] IN (
   WITH RECURSIVE typeoids(typoid) AS
     ( SELECT 'citext'::pg_catalog.regtype UNION
@@ -125,7 +131,8 @@ WHERE indclass[1] IN (
   WHERE opcintype = typeoids.typoid
 );
 
-UPDATE pg_catalog.pg_index SET indcollation[2] = 100
+UPDATE pg_catalog.pg_index SET indcollation =
+  pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[2] IN (
   WITH RECURSIVE typeoids(typoid) AS
     ( SELECT 'citext'::pg_catalog.regtype UNION
@@ -135,7 +142,8 @@ WHERE indclass[2] IN (
   WHERE opcintype = typeoids.typoid
 );
 
-UPDATE pg_catalog.pg_index SET indcollation[3] = 100
+UPDATE pg_catalog.pg_index SET indcollation =
+  pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[3] IN (
   WITH RECURSIVE typeoids(typoid) AS
     ( SELECT 'citext'::pg_catalog.regtype UNION
@@ -145,7 +153,8 @@ WHERE indclass[3] IN (
   WHERE opcintype = typeoids.typoid
 );
 
-UPDATE pg_catalog.pg_index SET indcollation[4] = 100
+UPDATE pg_catalog.pg_index SET indcollation =
+  pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[4] IN (
   WITH RECURSIVE typeoids(typoid) AS
     ( SELECT 'citext'::pg_catalog.regtype UNION
@@ -155,7 +164,8 @@ WHERE indclass[4] IN (
   WHERE opcintype = typeoids.typoid
 );
 
-UPDATE pg_catalog.pg_index SET indcollation[5] = 100
+UPDATE pg_catalog.pg_index SET indcollation =
+  pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[5] IN (
   WITH RECURSIVE typeoids(typoid) AS
     ( SELECT 'citext'::pg_catalog.regtype UNION
@@ -165,7 +175,8 @@ WHERE indclass[5] IN (
   WHERE opcintype = typeoids.typoid
 );
 
-UPDATE pg_catalog.pg_index SET indcollation[6] = 100
+UPDATE pg_catalog.pg_index SET indcollation =
+  pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+ \\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[6] IN (
   WITH RECURSIVE typeoids(typoid) AS
     ( SELECT 'citext'::pg_catalog.regtype UNION
@@ -175,7 +186,8 @@ WHERE indclass[6] IN (
   WHERE opcintype = typeoids.typoid
 );
 
-UPDATE pg_catalog.pg_index SET indcollation[7] = 100
+UPDATE pg_catalog.pg_index SET indcollation =
+  pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+ \\d+ \\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[7] IN (
   WITH RECURSIVE typeoids(typoid) AS
     ( SELECT 'citext'::pg_catalog.regtype UNION