iso14651_t1_common: make the fourth level the codepoint for characters which are...

iso14651_t1_common: make the fourth level the codepoint for characters which are ignorable on all 4 levels

Entries for characters which have “IGNORE” on all 4 levels like:

 <U0001> IGNORE;IGNORE;IGNORE;IGNORE % START OF HEADING (in ISO 6429)

are changed into:

 <U0001> IGNORE;IGNORE;IGNORE;<U0001> % START OF HEADING (in ISO 6429)

i.e. putting the code point of the character into the fourth level
instead of “IGNORE”. Without that change, all such characters
would compare equal which would make a wcscoll test case fail.
It is better to have a clearly defined sort order even for characters
like this so it is good to use the code point as a tie-break.

	* localedata/locales/iso14651_t1_common: Use the code point of a
        character in the fourth collation level instead of IGNORE for all
        entries which have IGNORE on all 4 levels.