Removing useless #include's.

Hello.

While looking some patch, just from curiosity, I checked for
redundant #include's in the source tree (except
contrib). "redundant" here means that a file is included in
another include file nearby.

I found 641 includes that is just removable with no side effect
with two exceptions.

- src/common/saslprep.c

  A comment that suggests linking wchar.c was placed just above
  '#include "mb/pg_wchar.h" but it is now just above "#include
  "common/unicode_norm.h" but the comment seems to be used as is.

 
- backend/storage/lmgr/spin.c

  spin.c and spin.h don't aggree on the necessity of pg_sema.h
  when HAVE_SPINLOCKS is defined. I post a mail about this issue
  separately.

regards,

-- 
Kyotaro Horiguchi
NTT Open Source Software Center