pgsql: Teach PostgresVersion all the ways to mark non-release code

Teach PostgresVersion all the ways to mark non-release code

As well as 'devel' version_stamp.pl provides for 'alphaN'
'betaN' and 'rcN', so teach PostgresVersion about those.

Also stash the version string instead of trying to reconstruct it during
stringification.

Discussion: https://postgr.es/m/YIHlw5nSgAHs4dK1@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/aa271209f6d995488fc5cba9731415f974823990

Modified Files
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src/test/perl/PostgresVersion.pm | 36 ++++++++++++++++++------------------
1 file changed, 18 insertions(+), 18 deletions(-)