lib/sh/db.sh: pg_dump(): ignore "No matching tables were found" error, using new ignore_err_msg()

lib/sh/util.sh: added ignore_err_msg()

lib/sh/db.sh: pg_schema_exists(): documented that `try` is used to suppress the error exit status

lib/sh/util.sh: stderr_matches(): usage: surrounded command in if statement to indicate what context it would usually be used in

lib/sh/make.sh: remaking alias: documented that you MUST use set_make_vars at the beginning of any function that uses this, so that $_remake is properly set to $remake and not left at its previous value

moved everything into /trunk/ to create the standard svn layout, for use with tools that require this (eg. git-svn). IMPORTANT: do NOT do an `svn up`. instead, re-use your working copy's existing files with `svn switch` (http://svnbook.red-bean.com/en/1.6/svn.ref.svn.c.switch.html).

fix: lib/sh/util.sh: verbosity_min(): usage: clarified that '' is a special value that causes $verbosity to be overwritten to ''

lib/sh/local.sh: public_schema_exists(): use a higher log_level for pg_schema_exists, to avoid all the verbose output involved in running the query

bugfix: lib/sh/local.sh: public_schema_exists(): can no longer use psql_script_vegbien for this, because using `SET search_path` (called by psql_script_vegbien) with a schema that does not exist no longer produces an error. instead, use new pg_schema_exists(), which uses a different command that does produce an error if the schema does not exist.

lib/sh/db.sh: added pg_require_schema()