pgsql: Show ignored constants as "$N" rather than "?" in pg_stat_statem

Show ignored constants as "$N" rather than "?" in pg_stat_statements.

The trouble with the original choice here is that "?" is a valid (and
indeed used) operator name, so that you could end up with ambiguous
statement texts like "SELECT ? ? ?". With this patch, you instead
see "SELECT $1 ? $2", which seems significantly more readable.
The numbers used for this purpose begin after the last actual $N parameter
in the particular query. The conflict with external parameters has its own
potential for confusion of course, but it was agreed to be an improvement
over the previous behavior.

Lukas Fittl

Discussion: https://postgr.es/m/CAP53PkxeaCuwYmF-A4J5z2-qk5fYFo5_NH3gpXGJJBxv1DMwEw@mail.gmail.com

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/a6f22e83562d8b78293229587cd3d9430d16d466

Modified Files
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.../expected/pg_stat_statements.out | 113 ++++++++++++++-------
contrib/pg_stat_statements/pg_stat_statements.c | 40 ++++++--
.../pg_stat_statements/sql/pg_stat_statements.sql | 16 ++-
doc/src/sgml/pgstatstatements.sgml | 29 ++++--
4 files changed, 142 insertions(+), 56 deletions(-)