Sparse-Uint: bug fix & added performance tests

This PR does:
- fix a bug in getindex_general.  Indexing with a disordered
  array lead to a no-methods error. Test added
- temprary fix for #7197 in `test/sparse.jl`
- added performance tests for Sparse-uint matrices
Merge pull request #7201 from mauro3/sparse_perf_bug1

Sparse-Uint: bug fix & added performance tests