Renamed "string" typedef in dynamic_buffer.h to avoid unneccesary name clashes.

Rev: src/dynamic_buffer.c:1.22
Rev: src/dynamic_buffer.h:1.17
Rev: src/modules/Mysql/mysql.c:1.60
Rev: src/modules/Mysql/result.c:1.28
Rev: src/modules/sprintf/sprintf.c:1.98
Rev: src/svalue.c:1.148