Spike detector precision implicit setting and variable name

[sepehrmn]

Two improvements:

1. "user_set_precise_times" is currently used to store whether the precise_times property been directly set and "precision" of the recording_device the actual value. By changing to "has_user_set_precise_times", one could readily understand the point of this variable without wasting time.
2. By setting "precision" one is implicitly setting the value of the variable above so in the set method it is necessary to set it to true if "precision" is directly set.

[sepehrmn]

I suggest @abigailm as a reviewer.

[heplesser]

This is an extended version of #431; I suggest to close that one.

[heplesser]

I don't agree with this name change, I think the original name is sufficiently clear (note that "set" is past tense in the original name).

[sepehrmn]

Dear Hans-Ekkehard, the first time I saw it, I read "user_set" word as a compound adjective. I will revert this change.

[heplesser]

@sepehrmn I don't understand what you want to achieve with your changes. Could you describe the use case you are trying to address?

[sepehrmn]

There are two issue left, the discrepancy in setting the value of precision and the default value of "precision". In #431 I offered a solution for the latter, but as @heplesser pointed out, it was not a good one. I try to offer a better one with a new pull request.

If there are precise models, and a user sets "precise_times" to true, everything goes fine. But if there are precise models and it is not set, there can be a few problems:

1. The precision value set by the user is ignored and it is set to 15. NEST does give the warning message below and it prints the value set, but it does not directly point to why the specified "precision" value was ignored and how one can set it to other than 15. "precision" is not exclusive to precise models. I will push a fix for this.

   Precise neuron models exist: the property precise_times of the
   spike_detector with gid 2 has been set to true, precision has been set to
   15.

2. The default precision is 3 on recording_device, but if precise models exist and "precise times" is not set, spike_detector deviates from this and sets it to 15. A warning is printed, but would it not make sense for everything to be consistent and only have 1 default value to exist? It makes sense to use a higher precision for precise models as pointed out in Changed default "precision" value of recording_device #431 , so a new pull request I will submit will have value 3 as default if no precise models exist and 15 if they do and user has not set the precision directly.

[sepehrmn]

This has morphed into #446 so I am closing it. Thanks @heplesser !