pgsql: Tweak FOR UPDATE/SHARE error message wording (again)

Tweak FOR UPDATE/SHARE error message wording (again)

In commit 0ac5ad5134 I changed some error messages from "FOR
UPDATE/SHARE" to a rather long gobbledygook which nobody liked. Then,
in commit cb9b66d31 I changed them again, but the alternative chosen
there was deemed suboptimal by Peter Eisentraut, who in message
1373937980(dot)20441(dot)8(dot)camel(at)vanquo(dot)pezone(dot)net proposed an alternative
involving a dynamically-constructed string based on the actual locking
strength specified in the SQL command. This patch implements that
suggestion.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/5712eeb2e7cf8e4236acffd4a403e7f14a48866f

Modified Files
--------------
src/backend/optimizer/plan/initsplan.c | 6 +-
src/backend/optimizer/plan/planner.c | 6 +-
src/backend/parser/analyze.c | 127 +++++++++++++++++++++++++++-----
src/include/parser/analyze.h | 1 +
4 files changed, 118 insertions(+), 22 deletions(-)