pgsql: Fix incorrect ordering of operations in pg_resetwal and pg_rewin

Fix incorrect ordering of operations in pg_resetwal and pg_rewind.

Commit c37b3d08c dropped its added GetDataDirectoryCreatePerm call into
the wrong place in pg_resetwal.c, namely after the chdir to DataDir.
That broke invocations using a relative path, as reported by Tushar Ahuja.
We could have left it where it was and changed the argument to be ".",
but that'd result in a rather confusing error message in event of a
failure, so re-ordering seems like a better solution.

Similarly reorder operations in pg_rewind.c. The issue there is that
it doesn't seem like a good idea to do any actual operations before the
not-root check (on Unix) or the restricted token acquisition (on Windows).
I don't know that this is an actual bug, but I'm definitely not convinced
that it isn't, either.

Assorted other code review for c37b3d08c and da9b580d8: fix some
misspelled or otherwise badly worded comments, put the #include for
<sys/stat.h> where it actually belongs, etc.

Discussion: https://postgr.es/m/aeb9c3a7-3c3f-a57f-1a18-c8d4fcdc2a1f@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1d96c1b91a4b7da6288ee63671a234b557ff5ccf

Modified Files
--------------
src/backend/storage/file/fd.c | 8 ++++----
src/backend/utils/init/globals.c | 4 +---
src/bin/pg_resetwal/pg_resetwal.c | 14 +++++++-------
src/bin/pg_rewind/pg_rewind.c | 20 ++++++++++----------
src/common/file_perm.c | 3 +--
src/include/common/file_perm.h | 4 +++-
6 files changed, 26 insertions(+), 27 deletions(-)