allow context cancellation in WAIT

[Pangoraw]

While investigating issue #518, I noticed that when pressing CTRL+C during WAIT() would not cause the program to stop instantly, but only at the end of the duration. You can now press CTRL+C when waiting and the stopping will happen instantly.

NOTE: I am not sure about the error message and whether or not I should add a test.

[codecov]

Codecov Report

Merging #524 into master will increase coverage by 0.0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #524   +/-   ##
======================================
  Coverage    41.8%   41.9%           
======================================
  Files         243     243           
  Lines        9069    9069           
======================================
+ Hits         3793    3797    +4     
+ Misses       4918    4916    -2     
+ Partials      358     356    -2     

[ziflex]

Almost perfect :)

[ziflex]

Good catch!

[Pangoraw]

This test started to fail randomly because the error message was changing from either core.ErrTerminated to context canceled: WAIT(1000). So in order to make sure the context was already canceled, I cancel it before running the program (see 70650cd).