pstext -D[j|J] is broken

[Chuan1937]

Add additional check for MC position in gmt_support.

Fixes: #8712
Refixing: #8916

The local test was successful:

The following tests passed:
        doc/scripts/GMT_pstext_clearance.sh
        doc/scripts/GMT_pstext_justify.sh
        test/pstext/ISO-8859-2.sh
        test/pstext/book.sh
        test/pstext/boxtext.sh
        test/pstext/caption.sh
        test/pstext/cliptxtbox.sh
        test/pstext/composite.sh
        test/pstext/corner_justify.sh
        test/pstext/delay.sh
        test/pstext/escape.sh
        test/pstext/filled_font.sh
        test/pstext/labeler.sh
        test/pstext/para_offset.sh
        test/pstext/pstext-l2s.sh
        test/pstext/shade_text.sh
        test/pstext/supersub.sh
        test/pstext/textclip.sh
        test/pstext/utf8.sh

100% tests passed, 0 tests failed out of 19

Total Test time (real) =  16.27 sec

[joa-quim]

I still have local failures that seem to be related to this. For example,

        799 - test/psbasemap/radial_labels1.sh (Failed)
        800 - test/psbasemap/radial_labels2.sh (Failed)
        801 - test/psbasemap/radial_labels3.sh (Failed)

They fail because text strings are a bit out of place when compared with references.

[Chuan1937]

I still have local failures that seem to be related to this. For example,

        799 - test/psbasemap/radial_labels1.sh (Failed)
        800 - test/psbasemap/radial_labels2.sh (Failed)
        801 - test/psbasemap/radial_labels3.sh (Failed)

They fail because text strings are a bit out of place when compared with references.

Need to run all the tests, right. I've only run examples related to pstext before. So there are omissions.