lib/sh/util.sh: shadow_fd(): don't require it to be run with log++ and instead let callers apply log++ if needed. in set_global_fds(), log++ can just be applied once for all the shadow_fd() calls.

lib/sh/util.sh: shadow_fd(): instead of applying minor=1 (i.e. an additional log++) to echo_func and then log++ again separately to set_fd, just apply it to the entire function

lib/sh/util.sh: set_fd(): don't increase the log_level for this function, and instead let callers increase it if needed

lib/sh/util.sh: limit_stderr(): inlined log++ with the can_log call because it should only apply to it. this also makes it obvious that log++ should not apply outside of this function. this also enables the contents of this function to be used in an alias.

lib/sh/util.sh: command(): use exec instead of `builtin command` to avoid spawning an extra process (since a subshell is already open)

bugfix: lib/sh/util.sh: command(): only indent if command was logged

bugfix: lib/sh/util.sh: .(): only indent if include statement was logged

lib/sh/util.sh: limit_stderr(): moved $stdout2stderr to command() so that limit_stderr()'s only purpose is to log-limit stderr

bugfix: lib/sh/util.sh: limit_stderr(): moved $stderr_is_errors default to command() where it's used

lib/sh/util.sh: limit_stderr(): do stdout2stderr after limit_stderr to avoid having two similar `can_log ... >/dev/null` commands