Remove zero- and one-argument range constructor functions.

Tom Lane <tgl@sss.pgh.pa.us>

Commit: df73584431e7edb1dd76578777bd0fcc17b916a1
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: 2011-11-23T01:45:05Z
Releases: 9.2.0
Remove zero- and one-argument range constructor functions.

Per discussion, the zero-argument forms aren't really worth the catalog
space (just write 'empty' instead).  The one-argument forms have some use,
but they also have a serious problem with looking too much like functional
cast notation; to the point where in many real use-cases, the parser would
misinterpret what was wanted.

Committing this as a separate patch, with the thought that we might want
to revert part or all of it if we can think of some way around the cast
ambiguity.

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