PR lib/54510: Fix file completion inside quotes which broke in rev 1.53

While there also fix handling character appending in the file completions when
inside quotes. For example when inside a quote, if the completion is a directory then
append a '/' but don't close the quote. On the other hand when inside a quote if the
completion is a file name and it is the only match then we can close the quote.

Perform quoting of filename completions when there are multiple matches as well

Quoting of special characters in filename completion was implemented for single match
case, this enables it for multiple matches as well. For example:

$ touch 'foo bar'
$ touch 'foo baz'
$ ls fo<TAB>
autocompletes to =>
$ ls foo\ ba
hitting <TAB> again shows:
foo bar foo baz

This required unescaping escape sequences generated during last completion
in order to find the word to complete.

While there, also update the test to include cases for multiple matches.

Reviewed by christos

branches: 1.3.2;
Handle filename autocompletion when the cursor is at a backslash or quote character

For example, handle following case:
$ touch 'foo bar'
$ ls foo\<TAB> --> $ ls foo\ bar

Also add test cases for this.

Thanks to Christos for review

branches: 1.2.2;
Add copyright and rcs header to the test program.
Also, remove a test case which was not supposed to be there.
(While that test case works with the changes I committed, testing that
test case with the test program is not possible in its current form. I'm
working on that.)

Add support for escaping special characters when doing filename completion.

For instance if the file name is "foo bar":
$ ls foo<TAB>
should get autocompleted to:
$ ls foo\ bar

Works for similar other characters too, which need escaping.

Also, add an accompanying test program to ensure the escaping is correct
in various scenarios (within quotes, without quotes, with other special characeters)

Thanks to Christos for reviews, help and feedback.

Perform quoting of filename completions when there are multiple matches as well

Quoting of special characters in filename completion was implemented for single match
case, this enables it for multiple matches as well. For example:

$ touch 'foo bar'
$ touch 'foo baz'
$ ls fo<TAB>
autocompletes to =>
$ ls foo\ ba
hitting <TAB> again shows:
foo bar foo baz

This required unescaping escape sequences generated during last completion
in order to find the word to complete.

While there, also update the test to include cases for multiple matches.

Reviewed by christos

Handle filename autocompletion when the cursor is at a backslash or quote character

For example, handle following case:
$ touch 'foo bar'
$ ls foo\<TAB> --> $ ls foo\ bar

Also add test cases for this.

Thanks to Christos for review

branches: 1.2.2;
Add copyright and rcs header to the test program.
Also, remove a test case which was not supposed to be there.
(While that test case works with the changes I committed, testing that
test case with the test program is not possible in its current form. I'm
working on that.)

Add support for escaping special characters when doing filename completion.

For instance if the file name is "foo bar":
$ ls foo<TAB>
should get autocompleted to:
$ ls foo\ bar

Works for similar other characters too, which need escaping.

Also, add an accompanying test program to ensure the escaping is correct
in various scenarios (within quotes, without quotes, with other special characeters)

Thanks to Christos for reviews, help and feedback.

Add copyright and rcs header to the test program.
Also, remove a test case which was not supposed to be there.
(While that test case works with the changes I committed, testing that
test case with the test program is not possible in its current form. I'm
working on that.)

Add support for escaping special characters when doing filename completion.

For instance if the file name is "foo bar":
$ ls foo<TAB>
should get autocompleted to:
$ ls foo\ bar

Works for similar other characters too, which need escaping.

Also, add an accompanying test program to ensure the escaping is correct
in various scenarios (within quotes, without quotes, with other special characeters)

Thanks to Christos for reviews, help and feedback.