MCOL-2000 Process charset definitions in the ALTER TABLE .. ADD COLUMN
MCOL-2000 Yet another fixes for column charsets
* make respect for column (including table/db/server default) charsets
for the TEXT(n) fields
* round TEXT(n) column length up to the next default length of TEXT-like
subtypes, 255 (TINYTEXT), 65535 (TEXT) and so on up to 2100000000
(LONGTEXT)