pgsql: Improve documentation of struct ParseState.

Improve documentation of struct ParseState.

I got annoyed about how some fields of ParseState were documented in the
struct's block comment and some weren't; not all of the latter are trivial.
Fix that. Also reorder a couple of fields that seem to have been placed
rather randomly, or maybe with an idea of avoiding padding space; but there
are never so many ParseStates in existence at one time that we ought to
value pad space over readability.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/3c40594e6eeabb3a8ad22aee93de3a19c41efdc2

Modified Files
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src/include/parser/parse_node.h | 44 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 39 insertions(+), 5 deletions(-)