Cleanup textblock's strbuf implementation.
Cleanup textblock's strbuf implementation.

This should provide correct code in a simpler way by sharing some of
the common code among functions.

Tested with E17 basics, require some applications with extensive usage
of textblock manipulation to do validate results.


git-svn-id: de1cbd220ac9a29ed59a7cc342d87cbce0beeb96@33939 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33

antognolli/Evas,antognolli/Evas,antognolli/Evas,antognolli/Evas