Reduce NL_ARGMAX to 4096 to match Linux.

[brooks]

Summary

NL_ARGMAX is the maximum number of postional arguments supported by
pritnf(3). Prior to r308145 it was declared as 99 and not enforced.
r308145 added enforcement and increased the value to 64k.

Unfortunately, development versions of PostgreSQL used the system definition to allocate and
zero an NL_ARGMAX * 4 sized array on the stack of its snprintf
implementation with measureable performance impacts. This has been
fixed in new PostgreSQL versions, but it is possible that other programs suffer from this
problem.

A value of 4096 puts us on par with Linux and is certainly large enough
for any reasionable program.

Reported by: mjg

[mjg]

I got a confirmation this is only an issue in the development version - older postgres verisions have the code but don't use it.

Regardless, the value should drop.