just the significant fields of FunctionCallInfoData, rather than MemSet'ing
the whole struct to zero.  Unused positions in the arg[] array will
thereby contain garbage rather than zeroes.  This buys back some of the
performance hit from increasing FUNC_MAX_ARGS.  Also tweak tuplesort.c
code for more speed by marking some routines 'inline'.  All together
these changes speed up simple sorts, like count(distinct int4column),
by about 25% on a P4 running RH Linux 7.2.