BUG #1741: %i missing in snprintf implementation

The following bug has been logged online:

Bug reference:      1741
Logged by:          Tim Mauch
Email address:      tgmauch@yahoo.com
PostgreSQL version: 8.0.1 - 8.0.3
Operating system:   Redhat linux 8.0
Description:        %i missing in snprintf implementation
Details: 

The implementation of snprintf/vsnprintf in src/port/snprintf.c does not
allow the use of %i ( %d equivalent ).  This likely isn't a problem for
postgres itself, but when a program compiles with -lpq and the standard c
libraries are not previously included the use of %i in the format string of
snprintf causes segmentation faults.

This is easily fixed by adding "case 'i':" to the same block of code handled
by "case 'd':" and case 'D':" in the implementation.