This patch changes the input routines for float4, float8 and oid to
reject empty strings (rather than treating them as "0"). In 8.0 we issue
a warning about this behavior and indicate that the input will not be
accepted by a future release, so it seems reasonable to disallow the
input in 8.1. The patch also updates the regression tests.
Barring any objections, I'll apply this to HEAD tomorrow.
-Neil
