manual.texi - make mysql_debug() argument match prototype in mysql.h.

manual.texi	- make mysql_data_seek() second argument match
manual.texi	  prototype in mysql.h.
manual.texi	- fix missing @xref parens in function names.
manual.texi	- mysql_change_user(), mysql_character_set_name()
manual.texi	  were out of order in C API section.