Support case-sensitive identifier lookup in autocomplete and \d commands

[nineinchnick]

Right now, all lookups are case-sensitive. But it only should be done in this manner when the search pattern contains mixed case, and it should be case-insensitive otherwise (the default).

[jpalus]

Note that for Oracle I suppose it should work differently. Consider two tables:

CREATE TABLE test1 (id int);
CREATE TABLE "test2" (id int);

Then

SELECT * FROM te<Tab>

should present only following completions:

test1

Same for mixed case:

SELECT * FROM TEs<Tab>

To get case sensitive completion one needs to use quoting:

SELECT * FROM "tes<Tab>

and completion candidates need to include quote:

"test2"

In other words all following SELECTs are valid for test1:

SELECT * FROM test1;
SELECT * FROM TEST1;
SELECT * FROM TeSt1;

but for test2 only one is valid:

SELECT * FROM "test2";

Not really sure what offers readline but for te<Tab> following completions could be presented:

test1
"test2"

but readline would need to be convinced that "test2" is completion for te* and insert quoting.