schemas/util.sql: explain2notice(): added helper function explain2notice_msg() which can also be used individually

fix: schemas/util.sql: schema comment: noted that avoiding use of STRICT also makes functions much easier to troubleshoot, because they won't mysteriously do nothing if called with only NULL arguments, even when you have added debug-print statements

schemas/util.sql, vegbien.sql: do not declare any SQL-language functions as STRICT, because this prevents them from being inlined (as documented in the util schema comment). the STRICT qualifier has been preserved where its behavior is necessary, rather than just used for optimization.

fix: schemas/util.sql: schema comment: indicate that all SQL-language functions should never be declared STRICT, not just IMMUTABLE ones, since inlining is not limited to IMMUTABLE (or STABLE) functions (although constant folding is)

bugfix: schemas/util.sql: join_strs_transform(): added back STRICT qualifier because it must be declared STRICT to use the special handling of STRICT aggregating functions

schemas/util.sql: %==(anyelement, anyelement): needs to be declared STABLE instead of IMMUTABLE because it depends on the search_path (as described at http://vegpath.org/links/#PostgreSQL:%20Documentation:%209.3:%20Function%20Volatility%20Categories%20**)

web/links/index.htm: updated to Firefox bookmarks: PostgreSQL: difference between STABLE and IMMUTABLE: functions that depend on the search_path: clarified that the confusing effects of using IMMUTABLE for one of these functions are only noticeable if the function is called on only constant values in a PL/pgSQL function (in which case the wrong search_path (the one in effect at create time) will be used)

schemas/util.sql, vegbien.sql: do not declare IMMUTABLE SQL-language functions as STRICT, because this prevents them from being inlined (as documented in the util schema comment)

web/links/index.htm: updated to Firefox bookmarks: PostgreSQL: added explanation of the difference between STABLE and IMMUTABLE, and common pitfalls in using IMMUTABLE when you should use STABLE. svn: added troubleshooting steps for running `svn upgrade` after the last Mac system update, which upgrades svn.

fix: schemas/util.sql: diff(text, text): use util.typeof() instead of pg_typeof() so the outputted query is runnable in any search_path