pgsql: Fix compatibility of pg_basebackup -R with 11 and olderversions

Fix compatibility of pg_basebackup -R with 11 and older versions

When 2dedf4d9 has integrated recovery.conf into postgresql.conf, it also
changed pg_basebackup -R in the way recovery configuration is
generated.  However this implementation forgot the fact that
pg_basebackup needs to keep compatibility with older server versions as
well.

Reported-by: Devrim Gündüz
Author: Sergei Kornilov, Michael Paquier
Discussion: https://postgr.es/m/3458f7cd12d74acd90180a671c8d5a081d60e162.camel@gunduz.org

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/beeb8e2e0717065296dc7b32daba2d66f0f931dd

Modified Files
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src/bin/pg_basebackup/pg_basebackup.c | 109 +++++++++++++++++++++++++---------
1 file changed, 82 insertions(+), 27 deletions(-)