Fix #133, remove_constraints!(opt) doesn't work; chkn() not defined

[sjvrensburg]

Proposed fix for issue #133

Purpose

The purpose of this pull request is to fix issue #133. Currently, remove_constraints!(opt) produces the following error:

UndefVarError: chkn not defined

Stacktrace:
 [1] remove_constraints!(::Opt) at /Users/myname/.julia/packages/NLopt/eqN9a/src/NLopt.jl:457
 [2] top-level scope at In[13]:1

The problem is that there is no function named chkn.

Proposal

It appears that the intention of the missing function is to check for any errors thrown by NLopt. The function chk already does this. Therefore, I have simply redefined remove_constraints! to use chk instead of chkn.

Additional Notes

I have also included a test file, fix133.jl, where I test remove_constraints!(::Opt).

Please note that I'm not a Julia expert and this is my first ever pull request. So, I'm not too sure whether I've done this PR thing correctly. Any constructive feedback will be much appreciated.

[stevengj]

LGTM. Nice PR!

I think chkn was from the older error handling method in NLopt, and this call was somehow overlooked when we updated to the new mechanism that requires us to pass the Opt object in order to get an error message.