The attached patch makes Calc use big brackets in Big mode when the Unicode characters are available. This makes for prettier display which is sort of the point of using Big mode. It follows previous use of Unicode characters for square root and integral signs.

The code supports big versions of round, square and curly brackets. Big square brackets are currently only used for intervals and curly ones not at all (maybe they could be put to use for Stirling numbers of the second kind).

Matrices do not use big brackets but they probably should since it is standard mathematical notation.

As far as I can tell the only reasons for not applying this would be that it is common with fonts or terminals where this doesn't look good, or that the resulting formula isn't recognised by the embedded-mode parser (which is already the case with several other constructs).