Improve the test for chebfun.chebcoeffs().
Improve the test for chebfun.chebcoeffs().

The call to merge() in chebfun.chebcoeffs() prevented this test from testing
extraction of coefficients for a function with a breakpoint like it said it
was.  This is now fixed, and we've also added tests to check that things are
working properly with array-valued chebfuns.

alshedivat/chebfun,ilovejs/chebfun