Added a lot of missing PMOD_EXPORT.

Rev: src/array.h:1.30
Rev: src/backend.h:1.10
Rev: src/callback.h:1.11
Rev: src/dynamic_buffer.h:1.11
Rev: src/errors.h:1.15
Rev: src/fdlib.h:1.37
Rev: src/pike_error.h:1.5