Merge pull request #597 from weese/feature/stream-fixes

[TEST] added tests for creating an index of ModifiedString
[FIX] fixed test_arg_parse and test_index_base
[FIX] Stream: added non-const char * write()
Merge pull request #599 from esiragusa/fix/stream/chunking

[FIX] Stream: added non-const char * write()
[FIX] fixed ngs_roi and bs_tools tests
Merge branch 'develop' of github.com:seqan/seqan into feature/stream-fixes
[FIX] fixed test_index_vstree