lib/sh/db.sh: mysql_cmd(): removed set_database because this is now performed by each caller before they use $database

lib/sh/db.sh: mysql_cmd: get command name by adding $FUNCNAME in an alias instead of using ${FUNCNAME¹} in the function, so that callers can also call mysql_cmd via a nested function, etc.

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

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

lib/sh/util.sh: command alias: also prepend -- to args to prevent a first arg starting with -- from being interpreted as an option to the `command` builtin

lib/sh/db.sh: mysql_cmd(): moved setting of database to specific callers (mysql(), mysqldump()) because the syntax to set it differs between mysql* commands (e.g. mysql uses `--database=` while mysqldump uses `--databases ... --tables`)

lib/sh/db.sh: added set_database alias, and use it in mysql_cmd()

lib/sh/util.sh: import_vars alias and applicable aliases that use it: documented that when used inside another alias 2+ levels deep, it must be run inside a function. this is due to a strange bug in bash where $() expressions in 2-level aliases produce a syntax error when the alias is expanded outside a function.

bugfix: lib/sh/util.sh: added back missing echo_func alias, which is needed to also include "$@" in the echoed function call

lib/sh/util.sh: import_vars alias: use new get_prefix_vars()