[Ohrrpgce] SVN: teeemcee/8090 run_and_get_output can now also capture stderr; replace SHELL with it in

[subversion at HamsterRepublic.com]

teeemcee
2016-08-11 08:39:33 -0700 (Thu, 11 Aug 2016)
731
run_and_get_output can now also capture stderr; replace SHELL with it in spawn_and_wait and os_shell_move

stderr is debuginfo logged by default by run_and_get_output, can be disabled.

The latter two functions can now detect and return sensible error messages
if e.g. xterm is missing or mv/move fails.
But TODO: spawn_and_wait can report errors running xterm, but not the
command that xterm runs (or what its exit code is). Have to separately capture
stderr from that too!

run_and_get_output is the closest thing we have to an error-checking replacement
for SHELL, but it's not perfect since error codes aren't ideal (and FB 0.23
returns mangled ones) and the shell adds an extra layer that changes error
codes and can go wrong.
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U   wip/common.rbas
U   wip/util.bas
U   wip/util.bi