[FIX] Fixing includes in misc_union_find.h.
[FIX] Adding getValueById() for const owner StringSet.
Merge pull request #238 from holtgrewe/union_find_includes

[FIX] Includes in misc_union_find.h and getValueById for const Owner StringSet
Remove “unused typedef” warning
Merge branch 'develop' of https://github.com/seqan/seqan into develop