Code review for pg_verify_checksums.c.
Code review for pg_verify_checksums.c.

Use postgres_fe.h, since this is frontend code.  Pretend that we've heard
of project style guidelines for, eg, #include order.  Use BlockNumber not
int arithmetic for block numbers, to avoid misbehavior with relations
exceeding 2^31 blocks.  Avoid an unnecessary strict-aliasing warning
(per report from Michael Banck).  Const-ify assorted stuff.  Avoid
scribbling on the output of readdir() -- perhaps that's safe in practice,
but POSIX forbids it, and this code has so far earned exactly zero
credibility portability-wise.  Editorialize on an ambiguously-worded
message.

I did not touch the problem of the "buf" local variable being possibly
insufficiently aligned; that's not specific to this code, and seems like
it should be fixed as part of a different, larger patch.

Discussion: d8a04c983cbfe264684700f860a91db1a91f6875@credativ.de

adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,50wu/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb