Verify that current Reduce only removes both Histidine Hydrogens for two ionic bonds

[russell-taylor]

Jane thinks that the current code never tries removing a second hydrogen in the case where there is only one (perhaps by adding a penalty score for this). She thinks that they never take off both Hydrodens unless there are two ions.

If the Histidine can flip, then it can either have one or two hydrogens but not zero. It tests two flip states and three protonation states.

Verify with code inspection that this is true.

[russell-taylor]

There are entries for the no-hydrogen case listed at https://github.com/rlabduke/reduce/blob/master/reduce_src/FlipMemo.cpp#L165

However, these are only tried after extendOrientations() has been called and that never seems to be the case. So indeed it never tries the doubly deprotenated case when doing flip checking.

Presumably it does not insert a flipMemo when there is an ionic bond, but it certainly never checks this case when it is doing flips.