Make some parallelization in table-generator more fine-granular and thus more efficient.
Make some parallelization in table-generator more fine-granular and thus
more efficient.

Previously, all result XML files that were mentioned in a single
<result> tag were loaded sequentially, now we parallelize loading of all
result files across all <result> tags.

sosy-lab/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,dbeyer/benchexec,martin-neuhaeusser/benchexec,martin-neuhaeusser/benchexec,martin-neuhaeusser/benchexec,sosy-lab/benchexec,dbeyer/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,dbeyer/benchexec,dbeyer/benchexec,IljaZakharov/benchexec,sosy-lab/benchexec,IljaZakharov/benchexec,sosy-lab/benchexec,martin-neuhaeusser/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,IljaZakharov/benchexec,IljaZakharov/benchexec