pgsql: Measure string lengths only once

Measure string lengths only once

Bernd Helmle complained that CreateReplicationSlot() was assigning the
same value to the same variable twice, so we could remove one of them.
Code inspection reveals that we can actually remove both assignments:
according to the author the assignment was there for beauty of the
strlen line only, and another possible fix to that is to put the strlen
in its own line, so do that.

To be consistent within the file, refactor all duplicated strlen()
calls, which is what we do elsewhere in the backend anyway. In
basebackup.c, snprintf already returns the right length; no need for
strlen afterwards.

Backpatch to 9.4, where replication slots were introduced, to keep code
identical. Some of this is older, but the patch doesn't apply cleanly
and it's only of cosmetic value anyway.

Discussion: http://www.postgresql.org/message-id/BE2FD71DEA35A2287EA5F018@eje.credativ.lan

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/80ae841f2f0c51ea766a75f4abe73c0c48e4ab0c

Modified Files
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src/backend/replication/basebackup.c | 30 +++++++-----
src/backend/replication/walsender.c | 85 ++++++++++++++++++++--------------
2 files changed, 70 insertions(+), 45 deletions(-)