Anbangx/debug split repeat2

Eventually, fix the error showed in split repeat. Actually the error is not in split repeat, but it's in path merge. The graph becomes asymmetric after path merge..... Spend a lot time figuring out -- remote debug, symmetric checking, extract subgraph, logging.... And huge non-human-readable graph... Anyway, this bug is fixed. 

Some changes in this branch:
1. Make SymmetryCheck more useful. It will not only check if the corresponding edge exists, but also check if the EdgeMap is the same one(same EdgeType and same readIdSet).

2. Add log to Split Repeat.

@jakebiesinger @JavierJia @Nan-Zhang Have a look! Thanks.