Both dict_int and dict_xsyn were blithely assuming that whatever memory
palloc gives back will be pre-zeroed. This would typically work for
just about long enough to run their regression tests, and no longer :-(.
The pre-9.0 code in dict_xsyn was even lamer than that, as it would
happily give back a pointer to the result of palloc(0), encouraging
its caller to access off the end of memory. Again, this would just
barely fail to fail as long as memory contained nothing but zeroes.
Per a report from Rodrigo Hjort that code based on these examples
didn't work reliably.
by installing an error context subroutine that will provide the file name
and line number for all errors detected while reading a config file.
Some of the reader routines were already doing that in an ad-hoc way for
errors detected directly in the reader, but it didn't help for problems
detected in subroutines, such as encoding violations.
Back-patch to 8.3 because 8.3 is where people will be trying to debug
configuration files.
