keep native errors for umanaged collections

[DmytroSoninLinguahouse]

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• What
• Why

What

Change method monkey patching code to allow to return unaltered error message when collection isn't being validated and doesn't have any simplschema attached.

Why

collection2 monkey patches Collection class globally changing collection instances for the whole project even if they don't use collection2 functionalities.
For new collections we were using mongodb's native json schema validation, but errors returned by mongo are getting changed by collection2 and end up being unhelpful (it leaves the text message but strips any actual useful data from mongo error).
This pr makes presence of collection2 less intrusive for collections that don't use collection2 for validation

[harryadel]

The change itself is alright but 1) Why did you change the entire package setup? 2) Can you please add tests for your changes?

[DmytroSoninLinguahouse]

@harryadel oh, my bad. Second commit wasn't meant for pr, it was for my fork only

[harryadel]

if the current tests suit passes and you add a test case for your change then I'll gladly accept it :)

[harryadel]

Thank you @DmytroSoninLinguahouse I'm adding the tests and continuing the work here
#460

[DmytroSoninLinguahouse]

@harryadel much appreciated, you're a star :)
I had environment issues, couldn't run meteor locally to do tests, planned to make a dockerfile as workaround, but didn't find time for it.