[fsa] bug fix: random arc weights

I noticed a bug in fsa-0.9.4: when an XML file is read in which an arc has no weight specified then the weight will be uninitialized and may be a random value. The behavior occurred on an Intel(R) Xeon(TM) CPU 3.06GHz system, after compiling with gcc-3.4.4. For example, the arc weight in the src/Tools/Fsa/examples/closure-1.fsa machine is -1.792753, or -1.829887, different on every run, instead of 0. To fix the bug, insert the line arc_->weight_ = fsa_->semiring()->one(); in src/Fsa/StorageXml.cc, after line 97, so that you have arc_->output_ = Epsilon; arc_->weight_ = fsa_->semiring()->one(); --Markus