CopyReadAttributesCSV optimization

Here's a patch to speed up CopyReadAttributesCSV. On the test case I've
been playing with, loading the TPC-H partsupp table, about 20%
CopyReadAttributesCSV (inlined into DoCopy, DoCopy itself is insignificant):

samples % image name symbol name
8136 25.8360 postgres CopyReadLine
6350 20.1645 postgres DoCopy
2181 6.9258 postgres pg_verify_mbstr_len
2157 6.8496 reiserfs (no symbols)
1668 5.2968 libc-2.7.so memcpy
1142 3.6264 libc-2.7.so ____strtod_l_internal
951 3.0199 postgres heap_formtuple
904 2.8707 libc-2.7.so ____strtol_l_internal
619 1.9656 libc-2.7.so memset
442 1.4036 libc-2.7.so strlen
341 1.0828 postgres hash_any
329 1.0447 postgres pg_atoi
300 0.9527 postgres AllocSetAlloc

With this patch, the usage of that function goes down to ~13%

samples % image name symbol name
7191 28.7778 postgres CopyReadLine
3257 13.0343 postgres DoCopy
2127 8.5121 reiserfs (no symbols)
1914 7.6597 postgres pg_verify_mbstr_len
1413 5.6547 libc-2.7.so memcpy
920 3.6818 libc-2.7.so ____strtod_l_internal
784 3.1375 libc-2.7.so ____strtol_l_internal
745 2.9814 postgres heap_formtuple
508 2.0330 libc-2.7.so memset
398 1.5928 libc-2.7.so strlen
315 1.2606 postgres hash_any
255 1.0205 postgres AllocSetAlloc

The trick is to split the loop in CopyReadAttributesCSV into two parts,
inside quotes, and outside quotes, saving some instructions in both
parts.

Your mileage may vary, but I'm quite happy with this. I haven't tested
it much yet, but I wouldn't expect it to be a loss in any interesting
scenario. The code also doesn't look much worse after the patch, perhaps
even better.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com