[BUGFIX] Make TCA property "exclusiveKeys" work with single key

It is necessary that "exclusiveValues" is a string in the JavaScript
method FormEngine.setSelectOptionFromExternalSource() because
in JavaScript strings (but not numbers) have a method match() which
is used in FormEngine.setSelectOptionFromExternalSource().

"exclusiveValues" representing a single key (e.g. -1) are of type
"Number" - in this case an JavaScript error is thrown when the
script calls match() on it.

This commit ensures that "exclusiveValues" is always casted to
String.

Resolves: #61276
Releases: 6.3, 6.2
Change-Id: I049a5e6d11b3b27be901baa1e00429ab200b9a04
Reviewed-on: http://review.typo3.org/32591
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
[BUGFIX] indexed_search: in some cases indexing does not work

In some cases $pObj->register['SYS_LASTCHANGED'] is NULL and therefore
a MySQL error occurs during indexing a page. So, in these cases,
we need to set the 'mtime' value by getting it from the page and we
always want to prevent a NULL-value getting inserted into the DB.

Resolves: #61135
Releases: 6.1, 6.2, 6.3
Change-Id: Idb78af3aa23350db4bd43f58638541e6b3ad3ae3
Reviewed-on: http://review.typo3.org/32355
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>