lib/sh/make.sh: self_make(): documented that it should be preceded by set_make_vars

bugfix: inputs/GBIF/_MySQL/GBIFPortalDB-2013-02-20.data.sql.run: ^.preamble.sql/make(): need to run set_make_vars even though the make vars are not used, because set_make_vars sets $_remake, which is needed by self_make

lib/sh/make.sh: set_make_vars: echo_vars $_remake to help debugging

bugfix: lib/sh/util.sh: to_file(): need to run invoked cmd using redir so that >$stdout redir is applied properly when cmd is a shell function instead of an external command (external commands were already redirected properly because command() calls redir). this fixes a bug in inputs/GBIF/_MySQL/GBIFPortalDB-2013-02-20.data.sql.run ^.preamble.sql/make(), where the generated file would be output to stdout instead of to the file because to_file()'s command was a shell function, and therefore the redirection was not applied. this fix requires redir() to be a separate function from command(), because command() does many things that are only applicable to external commands.

lib/sh/util.sh: redir(): override save_e and add `unset redirs` so error handlers are not redirected

lib/sh/util.sh: added alias_append(), similar to func_override() for aliases

lib/sh/util.sh: redir(): don't do redir actions if redir will be run later (i.e. if command to run starts with `redir` or `command`)

lib/sh/util.sh: redir(), command(): log their function calls at the usual log_level (2) instead of one higher, so that they are printed in the call tree to help debugging

lib/sh/util.sh: added redir() and use it in command() to perform and echo the redirections

lib/sh/util.sh: command(): removed comment that "the following redirections must happen in exactly this order", because there is now only one redirection