pgsql: Add timeline ID to file names generated with pg_waldump --save-f

Add timeline ID to file names generated with pg_waldump --save-fullpage

Not including the timeline IDs to the file names generated by pg_waldump
for the individual blocks saved could cause some of these files to be
overwritten when scanning segments across multiple timelines.  Having
this information is also as much useful as the LSNs, to be able to know
from exactly which WAL segment a block is comes from.

While on it, this fixes a few comments in the tests, where the format of
the file was not described as matching with the reality.

Reported-by: Fujii Masao
Reviewed-by: Kyotaro Horiguchi, David Christensen
Discussion: https://postgr.es/m/ZJp921+nITFnvBVS@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b381d9637030c163c3b1f8a9d3de51dfc1b4ee58

Modified Files
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doc/src/sgml/ref/pg_waldump.sgml          | 9 ++++++++-
src/bin/pg_waldump/pg_waldump.c           | 3 ++-
src/bin/pg_waldump/t/002_save_fullpage.pl | 9 +++++----
3 files changed, 15 insertions(+), 6 deletions(-)