Document need to quote index columns

Due to the use of `pg_get_indexdef()`, which double-quotes them and we
simply compare them. Resolves #247.

Changes

@@ -8,6 +8,12 @@ Revision history for pgTAP
 * Added support for the date and time keywords `CURRENT_DATE`, `CURRENT_TIME`,
   `CURRENT_TIMESTAMP`, `LOCALTIME`, and `LOCALTIMESTAMP` to `col_default_is()`.
   Thanks to Kevin Brannen for the report (#244)!
+* Fixed failure to run tests on Postgres 13. Thanks to Christoph Berg for the
+  report (#248).
+* Documented that mixed-case column names created with double quotes
+  must be double-quoted when passed to `has_index()` or `is_indexed()`,
+  sadly unlike other column arguments in pgTAP. Thanks to Keith Fiske for
+  the report (#247).
 
 1.1.0 2019-11-25T19:05:38Z
 --------------------------

doc/pgtap.mmd

@@ -3517,6 +3517,20 @@ incorrect, the diagnostics will look more like this:
     #       have: "idx_baz" ON public.sometab(lower(name))
     #       want: "idx_baz" ON public.sometab(lower(lname))
 
+Note that unlike most other column parameter arguments in pgTAP, mixed-case
+column mames crated with double-quotes must be double-quoted when passed
+to `has_index()`, like so:
+
+    SELECT has_index(
+        'myschema',
+        'sometable',
+        'myindex',
+        ARRAY[ 'id', '"Name"', 'lower("foo-bar")' ]
+    );
+
+This caveat applies only to column names, not to table and schema names,
+which should omit double-quoting.
+
 ### `hasnt_index()` ###
 
     SELECT hasnt_index( schema, table, index, description );
@@ -5092,6 +5106,15 @@ index on the named table. Effectively like `has_index()` except that it
 doesn't require an index name and does require one or more column names or
 expressions in the defined for the index.
 
+Note that unlike most other column parameter arguments in pgTAP, mixed-case
+column mames crated with double-quotes must be double-quoted when passed
+to `is_indexed()`, like so:
+
+    SELECT is_indexed( 'widgets', '"Name"' );
+
+This caveat applies only to column names, not to table and schema names,
+which should omit double-quoting.
+
 ### `index_is_type()` ###
 
     SELECT index_is_type( :schema, :table, :index, :type, :description );