pgsql: doc: Clarify name of files generated by pg_waldump --save-fullpa

doc: Clarify name of files generated by pg_waldump --save-fullpage

The fork name is always separated with the block number by an underscore
in the names of the files generated, but the docs stuck them together
without a separator, which was confusing.

Author: Christoph Berg
Discussion: /messages/by-id/ZvxtSLiix9eceMRM@msg.df7cb.de
Backpatch-through: 16

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/506eede7111ae7c88bd3c21f653bbb65846bd4a5

Modified Files
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doc/src/sgml/ref/pg_waldump.sgml | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)