Added support for the charsetnr column attribute. Fixed proper recognition

of binary fields in unicode decode mode by using charsetnr instead of the
binary flag (which might be set for nonbinary columns too, e.g. "VARCHAR(17)
BINARY").

Unfortunately this means that unicode decode mode is disabled if Pike is
compiled with a client lib without support for the charsetnr attribute. That
means libs before 4.1.0.

Rev: lib/modules/Sql.pmod/mysql.pike:1.34
Rev: lib/modules/Sql.pmod/sql_util.pmod:1.16
Rev: src/modules/Mysql/acconfig.h:1.18
Rev: src/modules/Mysql/configure.in:1.54
Rev: src/modules/Mysql/mysql.c:1.107
Rev: src/modules/Mysql/result.c:1.37